Implemented detached check to i.js for public fields.

There are test cases where we do not want to call `simplify()` for public fields given that they are detached. When we are in `processDeclaration()`, we will now check if the declaration is detached and break out of the method so we do not call `simplify`. Unit tests have been added to show public field support.

PiperOrigin-RevId: 551272612

Author: Closure Team

src/com/google/javascript/jscomp/ijs/ConvertToTypedInterface.java

@@ -534,10 +534,10 @@ private static String rootName(String qualifiedName) {
     }
 
     private boolean shouldRemove(String name, PotentialDeclaration decl) {
+      if (decl.isDetached()) {
+        return true;
+      }
       if (rootName(name).startsWith("$jscomp")) {
-        if (decl.isDetached()) {
-          return true;
-        }
         // These are created by goog.scope processing, but clash with each other
         // and should not be depended on.
         if ((decl.getRhs() != null && decl.getRhs().isClass())

test/com/google/javascript/jscomp/ijs/ConvertToTypedInterfaceTest.java

@@ -87,6 +87,26 @@ public void testComputedFieldNoRHS() {
             "}"));
   }
 
+  @Test
+  public void testDoubleAssignmentField() {
+    test(
+        lines(
+            "let Snackbar = Snackbar1 = class Snackbar {", //
+            "  x = 5",
+            "}"),
+        "/** @const @type {UnusableType} */ var Snackbar;");
+  }
+
+  @Test
+  public void testDoubleAssignmentStaticField() {
+    test(
+        lines(
+            "let A = B = class C {", //
+            "  static y = true",
+            "}"),
+        "/** @const @type {UnusableType} */ var A;");
+  }
+
   @Test
   public void testSuperClassFields() {
     test(