build: support running compiler-cli tests on windows (#28550)

In order to support running "compiler-cli" tests that use the "test_support.ts"
utilities on Windows with Bazel, we need to imporve the logic that resolves NPM
packages and symlinks them into a temporary directory.

A more Bazel idiomatic and windows compatible way of resolving Bazel runfiles
is to use the "RUNFILES_MANIFEST" if present. This ensures that the NPM
packages can be also symlinked on Windows, and tests can execute properly
on Windows. Read more about why this is needed here:

* https://github.com/bazelbuild/bazel/issues/3726#issue-257062364

PR Close #28550

packages/compiler-cli/test/runfile_helpers.ts

@@ -0,0 +1,48 @@
+/**
+ * @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 fs from 'fs';
+import * as path from 'path';
+
+/**
+ * Gets all built Angular NPM package artifacts by querying the Bazel runfiles.
+ * In case there is a runfiles manifest (e.g. on Windows), the packages are resolved
+ * through the manifest because the runfiles are not symlinked and cannot be searched
+ * within the real filesystem.
+ */
+export function getAngularPackagesFromRunfiles() {
+  // Path to the Bazel runfiles manifest if present. This file is present if runfiles are
+  // not symlinked into the runfiles directory.
+  const runfilesManifestPath = process.env.RUNFILES_MANIFEST_FILE;
+
+  if (!runfilesManifestPath) {
+    const packageRunfilesDir = path.join(process.env.RUNFILES !, 'angular/packages');
+
+    return fs.readdirSync(packageRunfilesDir)
+        .map(name => ({name, pkgPath: path.join(packageRunfilesDir, name, 'npm_package/')}))
+        .filter(({pkgPath}) => fs.existsSync(pkgPath));
+  }
+
+  return fs.readFileSync(runfilesManifestPath, 'utf8')
+      .split('\n')
+      .map(mapping => mapping.split(' '))
+      .filter(([runfilePath]) => runfilePath.match(/^angular\/packages\/[\w-]+\/npm_package$/))
+      .map(([runfilePath, realPath]) => ({
+             name: path.relative('angular/packages', runfilePath).split(path.sep)[0],
+             pkgPath: realPath,
+           }));
+}
+
+/**
+ * Resolves a NPM package from the Bazel runfiles. We need to resolve the Bazel tree
+ * artifacts using a "resolve file" because the NodeJS module resolution does not allow
+ * resolving to directory paths.
+ */
+export function resolveNpmTreeArtifact(manifestPath: string, resolveFile = 'package.json') {
+  return path.dirname(require.resolve(path.posix.join(manifestPath, resolveFile)));
+}