Initial support for (thread ...) and (wait ...) in WAST (#8418)

* 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](https://github.com/WebAssembly/threads/tree/main/test/core/threads).
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.