Make it possible to use Path and friends on wasip2 without the so named feature (#1525)

* refactor(path): delegate implementations where possible

* feat(path): enable Path and friends on wasip2 without the feature

Unfortunately, `OsStrExt` and `OsStringExt` require the wasip2 feature
on wasip2 so we can't use `as_bytes()` on `OsStr` and friends. However,
the recommendation on the upstream issue [1] is to just use `to_str` as
WASI paths are unicode.

[1]: https://github.com/rust-lang/rust/issues/130323#issuecomment-2350430693