Add test case showing JSCompiler transpilation of class inheritance within a local scope

We could optionally simplify the output by detecting that C's constructor does not return a value, and producing:

let D = function() {
  C.apply(this, arguments);
}

Today this detection only works on globals/module exports, not function local classes.

This probably doesn't matter for normal code, but @closureUnaware code is always wrapped in a function.

PiperOrigin-RevId: 846298004

Author: lauraharker

test/com/google/javascript/jscomp/Es6RewriteClassTest.java

@@ -693,6 +693,30 @@ class C extends D { constructor(word) { super(word); } }
         """);
   }
 
+  @Test
+  public void testExtends_nonGlobalClass() {
+    test(
+        srcs(
+            """
+            function f() {
+              class C {}
+              class D extends C {}
+            }
+            """),
+        expected(
+            """
+            function f() {
+              /** @constructor */
+              let C = function() {};
+              /** @constructor */
+              let D = function() {
+                return C.apply(this, arguments) || this;
+              };
+              $jscomp.inherits(D, C);
+            }
+            """));
+  }
+
   @Test
   public void testExtendsExternsClass() {
     test(