Add WASI module to use instead of Glibc

[MaxDesiatov]

Since glibc and musl behave slightly differently, we wouldn't want our WASI users to type import Glibc believing they are actually getting glibc behaviour. Makes much more sense to implement a new Musl module that can be imported and used accordingly on WASI. Linux could benefit from this as well.

I'm currently trying to implement this in my swift-alpine repository, but any help and feedback here on possible different approaches is welcome as usual.

This should unblock apple#29871.

[MaxDesiatov]

Closing this as resolved in #1773 for swiftwasm-release/5.3 and in #1832 for swiftwasm.