Upstream wasi-types-generator-extra into wit-bindgen

[fschutt]

We need to remove lib/wasi-types/wasi-types-generator-extra/src/main.rs and upstream the functionality (bitflags support for repr(u16)) into wit-bindgen.

[fschutt]

Currently blocked because #3177 is not yet merged.

[syrusakbary]

Context: we would like to remove this code: https://github.com/wasmerio/wasmer/pull/3177/files#diff-8747a217eb303dd2584bcdc0796a5c82cb097ac73eb7655c8c49ecfe765fa45bR28-R51

And wit-bindgen doesn't seem to want to support the older repr: bytecodealliance/wit-bindgen#323

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

Feel free to reopen the issue if it has been closed by mistake.