fix(@angular/build): externalize Angular dependencies in Vitest runner

Marks common Angular packages and RxJS as external within the Vitest test runner's build configuration. This allows Vite to perform dependency pre-bundling on these libraries, which can significantly improve build and rebuild performance during test execution.

The implementation introduces a constant to hold the list of packages and merges them with any externalDependencies that may already exist in the base build options, preserving user configuration.

(cherry picked from commit 9f2d3f7)

Author: clydin

packages/angular/build/src/builders/unit-test/runners/vitest/build-options.ts

@@ -14,6 +14,21 @@ import { NormalizedUnitTestBuilderOptions, injectTestingPolyfills } from '../../
 import { findTests, getTestEntrypoints } from '../../test-discovery';
 import { RunnerOptions } from '../api';
 
+/**
+ * A list of Angular related packages that should be marked as external.
+ * This allows Vite to pre-bundle them, improving performance.
+ */
+const ANGULAR_PACKAGES_TO_EXTERNALIZE = [
+  '@angular/core',
+  '@angular/common',
+  '@angular/platform-browser',
+  '@angular/compiler',
+  '@angular/router',
+  '@angular/forms',
+  '@angular/animations',
+  'rxjs',
+];
+
 function createTestBedInitVirtualFile(
   providersFile: string | undefined,
   projectSourceRoot: string,
@@ -83,6 +98,11 @@ export async function getVitestBuildOptions(
   });
   entryPoints.set('init-testbed', 'angular:test-bed-init');
 
+  const externalDependencies = new Set(['vitest', ...ANGULAR_PACKAGES_TO_EXTERNALIZE]);
+  if (baseBuildOptions.externalDependencies) {
+    baseBuildOptions.externalDependencies.forEach((dep) => externalDependencies.add(dep));
+  }
+
   const buildOptions: Partial<ApplicationBuilderInternalOptions> = {
     ...baseBuildOptions,
     watch,
@@ -101,7 +121,7 @@ export async function getVitestBuildOptions(
     outputHashing: adjustOutputHashing(baseBuildOptions.outputHashing),
     optimization: false,
     entryPoints,
-    externalDependencies: ['vitest', '@vitest/browser/context'],
+    externalDependencies: [...externalDependencies],
   };
 
   buildOptions.polyfills = injectTestingPolyfills(buildOptions.polyfills);