std: Update dependency on `wasi` crate

This commit updates the crate dependency that the standard library has
on the `wasi` crate. This is now updated to depending explicitly on the
`wasip1` crate and the `wasip2` crate published on crates.io. These
crates are managed in the [same location][repo] as the `wasi` crate and
represent a different versioning scheme which doesn't require
multi-version WASI support to require depending on the same crate at
multiple versions. The code in libstd is updated to reference `wasip1`
and `wasip2` directly as well.

[repo]: https://github.com/bytecodealliance/wasi-rs