Remove need to use JSpecify's @nullable annotation (#1142)

Fixes #1139. There are real scenarios where projects may not want to
ship with a JSpecify dependence; see
#1139 (comment).
So, we remove any cases where we were specifically checking for or using
JSpecify's `@Nullable` annotation.

Most of the code changes are due to the fact that now, we check if an
annotation is a `@Nullable` annotation using
`Nullness.hasNullableAnnotation`, which requires a `Config` object as a
parameter. So we need to thread a `Config` object as a parameter through
a bunch of methods.

Author: msridhar

nullaway/src/main/java/com/uber/nullaway/generics/CheckIdenticalNullabilityVisitor.java

@@ -3,6 +3,7 @@
 import com.google.errorprone.VisitorState;
 import com.sun.tools.javac.code.Type;
 import com.sun.tools.javac.code.Types;
+import com.uber.nullaway.Config;
 import java.util.List;
 import javax.lang.model.type.NullType;
 import javax.lang.model.type.TypeKind;
@@ -14,9 +15,11 @@
  */
 public class CheckIdenticalNullabilityVisitor extends Types.DefaultTypeVisitor<Boolean, Type> {
   private final VisitorState state;
+  private final Config config;
 
-  CheckIdenticalNullabilityVisitor(VisitorState state) {
+  CheckIdenticalNullabilityVisitor(VisitorState state, Config config) {
     this.state = state;
+    this.config = config;
   }
 
   @Override
@@ -60,8 +63,8 @@ public Boolean visitClassType(Type.ClassType lhsType, Type rhsType) {
         // TODO Handle wildcard types
         continue;
       }
-      boolean isLHSNullableAnnotated = GenericsChecks.isNullableAnnotated(lhsTypeArgument, state);
-      boolean isRHSNullableAnnotated = GenericsChecks.isNullableAnnotated(rhsTypeArgument, state);
+      boolean isLHSNullableAnnotated = GenericsChecks.isNullableAnnotated(lhsTypeArgument, config);
+      boolean isRHSNullableAnnotated = GenericsChecks.isNullableAnnotated(rhsTypeArgument, config);
       if (isLHSNullableAnnotated != isRHSNullableAnnotated) {
         return false;
       }
@@ -91,8 +94,8 @@ public Boolean visitArrayType(Type.ArrayType lhsType, Type rhsType) {
     Type.ArrayType arrRhsType = (Type.ArrayType) rhsType;
     Type lhsComponentType = lhsType.getComponentType();
     Type rhsComponentType = arrRhsType.getComponentType();
-    boolean isLHSNullableAnnotated = GenericsChecks.isNullableAnnotated(lhsComponentType, state);
-    boolean isRHSNullableAnnotated = GenericsChecks.isNullableAnnotated(rhsComponentType, state);
+    boolean isLHSNullableAnnotated = GenericsChecks.isNullableAnnotated(lhsComponentType, config);
+    boolean isRHSNullableAnnotated = GenericsChecks.isNullableAnnotated(rhsComponentType, config);
     if (isRHSNullableAnnotated != isLHSNullableAnnotated) {
       return false;
     }