refactor(compiler-cli): expose `loadTestDirectory()` test helper (#36843)

This helper can be useful in other packages to load files from the
real disk into a mock file system.

PR Close #36843

packages/compiler-cli/test/helpers/BUILD.bazel

@@ -8,6 +8,7 @@ ts_library(
     srcs = glob([
         "**/*.ts",
     ]),
+    module_name = "@angular/compiler-cli/test/helpers",
     deps = [
         "//packages:types",
         "//packages/compiler-cli/src/ngtsc/file_system",

packages/compiler-cli/test/helpers/src/mock_file_loading.ts

@@ -66,7 +66,8 @@ export function loadFakeCore(fs: FileSystem, basePath: string = '/') {
  * @param directoryPath the path to the directory we want to load.
  * @param mockPath the path within the mock file-system where the directory is to be loaded.
  */
-function loadTestDirectory(fs: FileSystem, directoryPath: string, mockPath: AbsoluteFsPath): void {
+export function loadTestDirectory(
+    fs: FileSystem, directoryPath: string, mockPath: AbsoluteFsPath): void {
   readdirSync(directoryPath).forEach(item => {
     const srcPath = resolve(directoryPath, item);
     const targetPath = fs.resolve(mockPath, item);