Add some wasi-threads tests

[yamt]

(venv) spacetanuki% TOYWASM=~/git/toywasm/b/toywasm python3 test-runner/wasi_test_runner.py -t tests/wat/testsuite -r ~/git/toywasm/test/wasi-testsuite-adapter.py
Test wasi_threads_exit_nonmain_wasi passed
Test wasi_threads_exit_main_busy passed
Test wasi_threads_exit_main_wasi passed
Test wasi_threads_exit_nonmain_busy passed
Test wasi_threads_spawn passed
Test wasi_threads_exit_main_block passed
Test wasi_threads_exit_nonmain_block passed

===== Test results =====
Runtime: toywasm v0.0
Suite: WASI wat tests
  Total: 7
  Passed:  7
  Failed:  0

Test suites: 1 passed, 0 total
Tests:       7 passed, 0 total
(venv) spacetanuki% 

[yamt]

i've written these while implementing wasi-threads in toywasm.
but nothing in these tests is toywasm-specific as far as i know.

[loganek]

I'll review the tests in details after end of year holidays, but my initial thought was that this should for now live in https://github.com/WebAssembly/wasi-threads? In fact there's one basic test added there already: WebAssembly/wasi-threads#11

[yamt]

I'll review the tests in details after end of year holidays, but my initial thought was that this should for now live in https://github.com/WebAssembly/wasi-threads? In fact there's one basic test added there already: WebAssembly/wasi-threads#11

i haven't noticed that the "basic test" there was for the same test runner.
maybe i will move there.

[yamt]

moved to WebAssembly/wasi-threads#19