LibWeb: Add basic non-blocking Web-Locks

[boginw]

This PR introduces a basic non-blocking Web-locks.

No locking mechanism has been implemented, so acquiring a lock always immediately allows access to the exclusive zone. Leaving the actual locking mechanism and queue as future work.

Tests:

• web-locks/acquire.https.any.html passes 10 out of its 11 tests

  • The remaining failing test calls .request with a wrong number of arguments and expects the promise to reject, but the generated prototype throws a synchronus TypeError instead. Don't know how to handle that.

• web-locks/acquire.https.any.worker.html cannot run

  • Running it the browser shows that it also passes 10/11 tests, but I couldn't figure out how to properly import these, getting stuck on:

   Failed load of: "file:///web-locks/acquire.https.any.worker.js", Error: No such file or directory (errno=2), Duration: 0ms
  

• web-locks/lock-attributes.https.any.html passes 2 out of its 2 tests