Initial support for (thread ...) and (wait ...) in WAST

[stevenfontanella]

• Parse (thread ...) and (wait ...) in spec tests
  • Currently, we just run thread blocks directly, which means that wait is also a no-op. In the next PR, we'll add yield points on atomic operations e.g. memory.atomic.wait32.
  • We also disable splitting on tests that use (thread ...) for now. It should be possible to support this but we need better parsing in the module splitter. I'll add this in a future PR.
• Import threads tests from the threads repo. These currently aren't in the testsuite repo because the threads repo is far behind the upstream spec and has some merge conflicts.
• Passes 10/13 new spec tests.

Part of #8315 and #8261.

[tlively]

LGTM % comments.