test(elements): clean up TestStrategy between tests (#36114)

Previously, the `TestStrategy` `NgElementStrategy` used in
`createCustomElement()` tests was created once and re-used in each test
(due to complications related to how `customElements.register()` works).
As a result, the `TestStrategy` instance's state (e.g. inputs) could be
polluted from previous tests and affect subsequent ones.

This commit ensures the strategy instance is reset before each test.

PR Close #36114

packages/elements/test/create-custom-element_spec.ts

@@ -45,6 +45,8 @@ if (browserDetection.supportsCustomElements) {
           .then(done, done.fail);
     });
 
+    afterEach(() => strategy.reset());
+
     afterAll(() => destroyPlatform());
 
     it('should use a default strategy for converting component inputs', () => {
@@ -155,6 +157,12 @@ if (browserDetection.supportsCustomElements) {
       setInputValue(propName: string, value: string): void {
         this.inputs.set(propName, value);
       }
+
+      reset(): void {
+        this.connectedElement = null;
+        this.disconnectCalled = false;
+        this.inputs.clear();
+      }
     }
 
     class TestStrategyFactory implements NgElementStrategyFactory {