refactor(compiler-cli): implement BabelAstFactory and AstHosts (#38866)

This commit adds the `AstHost` interface, along with implementations for
both Babel and TS.

It also implements the Babel vesion of the `AstFactory` interface, along
with a linker specific implementation of the `ImportGenerator` interface.

These classes will be used by the new "ng-linker" to transform prelinked
library code using a Babel plugin.

PR Close #38866

packages/compiler-cli/linker/test/fatal_linker_error_spec.ts

@@ -0,0 +1,29 @@
+/**
+ * @license
+ * Copyright Google LLC 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 {FatalLinkerError, isFatalLinkerError} from '../src/fatal_linker_error';
+
+describe('FatalLinkerError', () => {
+  it('should expose the `node` and `message`', () => {
+    const node = {};
+    expect(new FatalLinkerError(node, 'Some message'))
+        .toEqual(jasmine.objectContaining({node, message: 'Some message'}));
+  });
+});
+
+describe('isFatalLinkerError()', () => {
+  it('should return true if the error is of type `FatalLinkerError`', () => {
+    const error = new FatalLinkerError({}, 'Some message');
+    expect(isFatalLinkerError(error)).toBe(true);
+  });
+
+  it('should return false if the error is not of type `FatalLinkerError`', () => {
+    const error = new Error('Some message');
+    expect(isFatalLinkerError(error)).toBe(false);
+  });
+});