Intent to prototype: WebAssembly multi-memory

[Ryan Hunt]

Summary:

    Allows a WebAssembly module to have access to more than one memory object. This is useful for merging independent modules together, or generating a module to mediate between two other modules (such as in a WebAssembly component-model proposal polyfill).

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1782585
Specification: https://github.com/WebAssembly/multi-memory/blob/main/proposals/multi-memory/Overview.md
Standards Body: WebAssembly CG (W3C)
Platform coverage: All platforms
Preference: javascript.options.wasm_multi_memory
DevTools bug: N/A
Other browsers:
    Blink: No signals
    WebKit: No signals
web-platform-tests: Covered by spec tests from upstream proposal.