Add a new Naga feature, `"compact"`, which adds a new function
`naga::compact::compact`, which removes unused expressions, types, and
constants from a `Module`.
Make changes suggested in #2075, but put off to a separate PR because they would interfere with reviewing the change:
- Split the new WGSL front end into modules in a logical way.
- Rename `Parser` to `Frontend`.
[Since Rust 1.58], Rust format strings have been able to "capture
arguments simply by writing {ident} in the string." Clippy 1.67 made
the corresponding warning, `uninlined_format_args`, warn-by-default.
Inlined arguments seem more readable, so Naga should adopt them.
[Since Rust 1.58]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1580-2022-01-13