refactor(ngcc): ensure unlocker process works in mock file-systems (#36989)

Previously the path to the unlocker process was being resolved by the
current file-system. In the case that this was a `MockFileSystemWindows`
on a non-Windows operating system, this resulted in an incorrect path
to the entry-point.

Now the path to the entry-point is hand-crafted to avoid being broken by
whatever FileSystem is in use.

PR Close #36989

packages/compiler-cli/ngcc/src/locking/lock_file_with_child_process/index.ts

@@ -78,7 +78,7 @@ export class LockFileWithChildProcess implements LockFile {
         this.logger.level !== undefined ? this.logger.level.toString() : LogLevel.info.toString();
     const isWindows = process.platform === 'win32';
     const unlocker = fork(
-        this.fs.resolve(__dirname, './unlocker.js'), [path, logLevel],
+        __dirname + '/unlocker.js', [path, logLevel],
         {detached: true, stdio: isWindows ? 'pipe' : 'inherit'});
     if (isWindows) {
       unlocker.stdout?.on('data', process.stdout.write.bind(process.stdout));