feat(compiler-cli): add support to extend angularCompilerOptions (#22717)

`TypeScript` only supports merging and extending of `compilerOptions`. This is an implementation to support extending and inheriting of `angularCompilerOptions` from multiple files.

Closes: #22684

PR Close #22717

packages/compiler-cli/test/perform_compile_spec.ts

@@ -0,0 +1,58 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import * as path from 'path';
+
+import {readConfiguration} from '../src/perform_compile';
+
+import {TestSupport, setup} from './test_support';
+
+describe('perform_compile', () => {
+  let support: TestSupport;
+  let basePath: string;
+
+  beforeEach(() => {
+    support = setup();
+    basePath = support.basePath;
+  });
+
+  function writeSomeConfigs() {
+    support.writeFiles({
+      'tsconfig-level-1.json': `{
+          "extends": "./tsconfig-level-2.json",
+          "angularCompilerOptions": {
+            "annotateForClosureCompiler": true
+          }
+        }
+      `,
+      'tsconfig-level-2.json': `{
+          "extends": "./tsconfig-level-3.json",
+          "angularCompilerOptions": {
+            "skipMetadataEmit": true
+          }
+        }
+      `,
+      'tsconfig-level-3.json': `{
+          "angularCompilerOptions": {
+            "annotateForClosureCompiler": false,
+            "annotationsAs": "decorators"
+          }
+        }
+      `,
+    });
+  }
+
+  it('should merge tsconfig "angularCompilerOptions"', () => {
+    writeSomeConfigs();
+    const {options} = readConfiguration(path.resolve(basePath, 'tsconfig-level-1.json'));
+    expect(options.annotateForClosureCompiler).toBe(true);
+    expect(options.annotationsAs).toBe('decorators');
+    expect(options.skipMetadataEmit).toBe(true);
+  });
+
+});