Start reusing rustc's `format_args` parser

[CohenArthur]

This pull request adds a base for reusing the rustc_format_parser crate to parse the format strings in format_args!() invocations. There are still a lot of things missing, and the build system stuff is probably wrong. The commit history needs to be fixed as well.

Fixes #2832

This PR depends on ~~#2802~~ #2853 for the proper libgrust Changelog file

[CohenArthur]

I'll open an issue to cleanup the implementation once it is merged, we can write better Rust in there and separate into better modules with better names.