rust: macros: use `quote!` from vendored crate

rust: macros: use `quote!` from vendored crate

With `quote` crate now vendored in the kernel, we can remove our custom
`quote!` macro implementation and just rely on that crate instead.

The `quote` crate uses types from the `proc-macro2` library so we also
update to use that, and perform conversion in the top-level lib.rs.

Clippy complains about unnecessary `.to_string()` as `proc-macro2`
provides additional `PartialEq` impl, so they are removed.

Reviewed-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Gary Guo <gary@garyguo.net>
Acked-by: David Gow <davidgow@google.com> # for kunit
Link: https://patch.msgid.link/20260112170919.1888584-3-gary@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>