Schedule initialization of JS context in a separate thread

[JaroslavTulach]

Pull Request Description

Implements the #5643 idea. As soon as MainModule creates Context for GraalVM execution, it schedules a background task to initialize JavaScript. The initialization finishes sooner than Enso compiler is ready to work, saving time when it is actually needed.

Important Notes

Only modifies boot sequence of MainModule (used in the IDE) and VerifyJavaScriptIsAvailableTest (to verify the "context passing logic" works OK between threads). Regular CLI execution remains unchanged for now assuming batch execution may not need JavaScript in all the cases and if it does the initialization speed isn't that critical.

Checklist

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the
  Scala,
  Java,
  style guides.
• All code has been tested:
  • Unit tests have been written where possible.

[JaroslavTulach]

Analysis of the new startup is available as comment in the original bug report.

[hubertp]

Sweet!

[JaroslavTulach]

Thank you for your review.

[enso-bot]

Jaroslav Tulach reports a new STANDUP for the last Friday (2023-02-17):

Progress: - Init JS context in a separate thread done: #5680

• triaging, review Warnings are discarded if a Nothing value crosses the polyglot boundary #5672
• talking about lucene-like index for libraries
• sharing exception handlers: Two findExceptionMessage methods to extract exception messages consistently #5684 It should be finished by 2023-02-17.

Next Day: Finish HostException handling