WASI phase 5: gap-suite subset under a WASI runtime in CI #11380

Part of #11375.

Run a subset of test-files/test_gap_*.ts compiled with --target wasi under the pinned WASI runtime, compared against the Node oracle like the native gap suite. Tests using child processes or real parallelism are excluded with a stated reason. Per the repo's gate rules: run it once green, then promote it; and assert the subject ran (e.g. the module actually executed under the WASI runtime, not a native fallback).