ie-js: expose WebAssembly global to JavaScript via Boa

[thomasnemer]

Goal

The wasmtime runtime (ie-wasm) works but isn't exposed as the WebAssembly JS global.

Current state

• WasmRuntime can instantiate .wasm modules from Rust
• No WebAssembly.instantiate() in JS
• No WebAssembly.Module/Instance/Memory JS classes

Implementation needed

• Register WebAssembly global object on JsRuntime
• WebAssembly.instantiate(bufferSource, importObject)
• WebAssembly.compile(bufferSource)
• Bridge between boa JsValue and wasmtime Val types

Impact

WebAssembly-heavy sites won't work. Low priority — most sites don't require wasm.