[browser] don't set js_handle for js prototypes (#115773)

Author: pavelsavara

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/JSImportTest.cs

@@ -20,6 +20,14 @@ public unsafe void StructSize()
             Assert.Equal(32, sizeof(JSMarshalerArgument));
         }
 
+        [Fact]
+        public unsafe void PrototypeNotEqual()
+        {
+            using var temp1 = JSHost.GlobalThis.GetPropertyAsJSObject("EventTarget");
+            using var temp2 = JSHost.GlobalThis.GetPropertyAsJSObject("Window");
+            Assert.NotEqual(temp1, temp2);
+        }
+
         [Fact]
         public async Task MultipleImportAsync()
         {

src/mono/browser/runtime/gc-handles.ts

@@ -81,7 +81,10 @@ export function mono_wasm_get_js_handle (js_obj: any): JSHandle {
     _cs_owned_objects_by_js_handle[<any>js_handle] = js_obj;
 
     if (Object.isExtensible(js_obj)) {
-        js_obj[cs_owned_js_handle_symbol] = js_handle;
+        const is_prototype = typeof js_obj === "function" && Object.prototype.hasOwnProperty.call(js_obj, "prototype");
+        if (!is_prototype) {
+            js_obj[cs_owned_js_handle_symbol] = js_handle;
+        }
     }
     // else
     //   The consequence of not adding the cs_owned_js_handle_symbol is, that we could have multiple JSHandles and multiple proxy instances.