Withdraw usages of java.io.Serial from the external repo.

They [break our JDiff setup](https://github.com/google/guava/actions/runs/13294400054/job/37123745397).

(followup to cl/726154745)

I should [finish setting up japicmp](google/error-prone#4311 (comment)), but for now, I want to unbreak publishing documentation for releases and snapshots.

(Some of the code formatting ends up a little odd because of how I'm stripping the annotations. We should be able to live with it until I can put the annotations back—or until we discover that they're causing problems _internally_ and need to withdraw them entirely :))

RELNOTES=n/a
PiperOrigin-RevId: 726521329

Author: cpovirk

android/guava-testlib/src/com/google/common/collect/testing/AbstractIteratorTester.java

@@ -27,7 +27,6 @@
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.J2ktIncompatible;
-import java.io.Serial;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -110,15 +109,15 @@ void assertPermitted(Exception exception) {
       }
     }
 
-    @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
   }
 
   private static final class UnknownElementException extends RuntimeException {
     private UnknownElementException(Collection<?> expected, Object actual) {
       super("Returned value '" + actual + "' not found. Remaining elements: " + expected);
     }
 
-    @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
   }
 
   /**

android/guava-testlib/src/com/google/common/collect/testing/BaseComparable.java

@@ -19,7 +19,6 @@
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.J2ktIncompatible;
-import java.io.Serial;
 import java.io.Serializable;
 import org.jspecify.annotations.Nullable;
 
@@ -57,5 +56,5 @@ public int compareTo(BaseComparable o) {
     return s.compareTo(o.s);
   }
 
-  @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
 }

android/guava-testlib/src/com/google/common/collect/testing/DerivedComparable.java

@@ -19,7 +19,6 @@
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.J2ktIncompatible;
-import java.io.Serial;
 
 /**
  * Simple derived class to verify that we handle generics correctly.
@@ -32,5 +31,5 @@ public DerivedComparable(String s) {
     super(s);
   }
 
-  @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
 }

android/guava-testlib/src/com/google/common/collect/testing/SafeTreeMap.java

@@ -18,7 +18,6 @@
 
 import com.google.common.annotations.GwtIncompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
-import java.io.Serial;
 import java.io.Serializable;
 import java.util.AbstractSet;
 import java.util.Collection;
@@ -326,5 +325,5 @@ public String toString() {
     return delegate.toString();
   }
 
-  @Serial private static final long serialVersionUID = 0L;
+  private static final long serialVersionUID = 0L;
 }

android/guava-testlib/src/com/google/common/collect/testing/SafeTreeSet.java

@@ -18,7 +18,6 @@
 
 import com.google.common.annotations.GwtIncompatible;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
-import java.io.Serial;
 import java.io.Serializable;
 import java.util.Collection;
 import java.util.Comparator;
@@ -254,5 +253,5 @@ public String toString() {
     return delegate.toString();
   }
 
-  @Serial private static final long serialVersionUID = 0L;
+  private static final long serialVersionUID = 0L;
 }

android/guava-testlib/src/com/google/common/collect/testing/features/ConflictingRequirementsException.java

@@ -19,7 +19,6 @@
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.J2ktIncompatible;
-import java.io.Serial;
 import java.util.Set;
 
 /**
@@ -52,5 +51,5 @@ public String getMessage() {
     return super.getMessage() + " (source: " + source + ")";
   }
 
-  @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
 }

android/guava-testlib/src/com/google/common/collect/testing/features/TesterRequirements.java

@@ -21,7 +21,6 @@
 import com.google.common.annotations.GwtCompatible;
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.J2ktIncompatible;
-import java.io.Serial;
 import java.util.Collections;
 import java.util.Set;
 import org.jspecify.annotations.Nullable;
@@ -81,5 +80,5 @@ public String toString() {
     return "{TesterRequirements: present=" + presentFeatures + ", absent=" + absentFeatures + "}";
   }
 
-  @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+  @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
 }

android/guava-testlib/src/com/google/common/collect/testing/google/BiMapInverseTester.java

@@ -25,7 +25,6 @@
 import com.google.common.collect.testing.Helpers;
 import com.google.common.collect.testing.features.CollectionFeature;
 import com.google.common.testing.SerializableTester;
-import java.io.Serial;
 import java.io.Serializable;
 import java.lang.reflect.Method;
 import java.util.Collections;
@@ -69,7 +68,7 @@ private static class BiMapPair<K, V> implements Serializable {
       this.backward = original.inverse();
     }
 
-    @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
   }
 
   /**

android/guava-testlib/test/com/google/common/testing/SerializableTesterTest.java

@@ -16,7 +16,6 @@
 
 package com.google.common.testing;
 
-import java.io.Serial;
 import java.io.Serializable;
 import junit.framework.AssertionFailedError;
 import junit.framework.TestCase;
@@ -78,11 +77,11 @@ public void testObjectWhichIsEqualButChangesClass() {
   }
 
   private static class ClassWhichDoesNotImplementEquals implements Serializable {
-    @Serial private static final long serialVersionUID = 1L;
+    private static final long serialVersionUID = 1L;
   }
 
   private static class ClassWhichIsAlwaysEqualButHasDifferentHashcodes implements Serializable {
-    @Serial private static final long serialVersionUID = 2L;
+    private static final long serialVersionUID = 2L;
 
     @SuppressWarnings("EqualsHashCode")
     @Override
@@ -92,7 +91,7 @@ public boolean equals(@Nullable Object other) {
   }
 
   private static class ObjectWhichIsEqualButChangesClass implements Serializable {
-    @Serial private static final long serialVersionUID = 1L;
+    private static final long serialVersionUID = 1L;
 
     @Override
     public boolean equals(@Nullable Object other) {

android/guava-tests/test/com/google/common/base/FunctionsTest.java

@@ -27,7 +27,6 @@
 import com.google.common.testing.EqualsTester;
 import com.google.common.testing.NullPointerTester;
 import com.google.common.testing.SerializableTester;
-import java.io.Serial;
 import java.io.Serializable;
 import java.util.Map;
 import junit.framework.TestCase;
@@ -369,7 +368,7 @@ public void testConstantSerializable() {
 
   private static class CountingSupplier implements Supplier<Integer>, Serializable {
 
-    @GwtIncompatible @J2ktIncompatible @Serial private static final long serialVersionUID = 0;
+    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
 
     private int value;