[WIP] ffi support

[manyuanrong]

FFI support based on libffi.

Related issues and PRs:

#8490
#7564

[lin7sh]

I think the big effort of Wasm and Wasi is keeping js away from ISA dependent binary code, why bring FFI back to make it complex again? I think someone could argue that they need FFI for low level hardware access, but it think it could provide by the runtime(browser or deno) itself for standardisation. Have a look of the new Web Serial API and Web NFC API in Chrome 89. A restricted but "run everywhere" is unique and is its strength for deno comparing to go and rust.

[bartlomieju]

Thank you for the PR @manyuanrong, we've been discussing FFI internally from time to time and will probably look into shipping it at some point. I'm gonna close this PR as it is stale and there's been a lot of changes to the ops interface since it was open, but we'll definitely circle back to it as a reference point if we decide to implement FFI.