wasm-bindgen rebase

We've been working on a rebase of the wasm-bindgen fork we maintain to produce javascript bindings for the client-side Lox wasm code. The fork is needed because the javascript bindings need to be run as an ESModule inside the browser, and so follows stricter rules than javascript that would be served to the user as part of a web page.

@onyinyang started a rebase. I opened this issue to document the current rebase process.