Add a utility for handling modules embedded in JS

[tlively]

Add a function that will search JS source for literal byte arrays that might contain Wasm modules. Handle skipping strings and comments, and handle signed and unsigned byte values in decimal, octal, and hex formats. Reject byte arrays that do not begin with the Wasm magic values, but do not otherwise verify that the bytes encode a well-formed or valid Wasm module.

Also add a function for printing a byte sequence as a JS byte array, formatted with 16 hex values per line.

A future PR will use these functions in wasm-reduce to reduce Wasm modules embedded in JS files.

[kripken]

This overlaps with

https://github.com/WebAssembly/binaryen/blob/main/scripts/clusterfuzz/extract_wasms.py

https://github.com/WebAssembly/binaryen/blob/main/scripts/clusterfuzz/embed_wasms.py

Is there a strong reason to justify this duplication?

[tlively]

No. It would make sense to deduplicate the logic. I would be happy to replace those scripts with a small new wasm-embed tool with an --extract option, or an arrangement similar to that. I still think using those scripts (or other similar scripts) as the well-lit path for running wasm-reduce on modules embedded in JS would be too complicated for folks who might want to do such reductions frequently but are not Binaryen developers.