WebAssembly source phase imports

[legendecas]

TC39 proposal source phase imports reached to stage 3 and has been implemented in V8 (starting from M131).

import source FooModule from "./foo.wasm";
FooModule instanceof WebAssembly.Module; // true

The feature requires Node.js integration to support WebAssembly source phase imports. TLDR, if a SourceTextModule imports a source-phase WebAssembly module, create a module source object with v8::WasmModuleObject::Compile and return the WebAssembly.Module object from v8::Module::ResolveSourceCallback, and v8::HostImportModuleWithPhaseDynamicallyCallback.

See design doc for details.

WPT: https://github.com/web-platform-tests/wpt/blob/master/wasm/webapi/esm-integration/source-phase.tentative.html

/cc @guybedford

[guybedford]

This should ideally be implemented along with the ESM instance imports and should likely also go with unflagging --experimental-wasm-modules.

[bakkot]

There's not much reason to care about ESM instance imports without also having worker_threads support instantiating workers from a ModuleSource - which is worth doing, but is probably a bigger topic than wasm source phase imports (which are immediately useful).

[sbc100]

Emscripten would love to start using this feature as soon as its available: emscripten-core/emscripten#23047