rust: macros: add `quote!` macro

Add the `quote!` macro for creating `TokenStream`s directly via the
given Rust tokens. It also supports repetitions using iterators.

It will be used by the pin-init API proc-macros to generate code.

Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-3-y86-dev@protonmail.com


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>