FROMLIST: rust: rbtree: add red-black tree implementation backed by the C version

The rust rbtree exposes a map-like interface over keys and values,
backed by the kernel red-black tree implementation. Values can be
inserted, deleted, and retrieved from a `RBTree` by key.

This base abstraction is used by binder to store key/value
pairs and perform lookups, for example the patch
"[PATCH RFC 03/20] rust_binder: add threading support"
in the binder RFC [1].

Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-3-08ba9197f637@google.com/

 [1]
Change-Id: I1de1370fef24bb6da71becec8c970f6804c75b6a
Signed-off-by: Wedson Almeida Filho <wedsonaf@gmail.com>
Signed-off-by: Matt Gilbride <mattgilbride@google.com>

Bug: 324206405
Link: https://lore.kernel.org/all/20240205-b4-rbtree-v1-2-995e3eee38c0@google.com/


Change-Id: I9a757633b14b9a142106200a44843e65f57369d2
Signed-off-by: Alice Ryhl <aliceryhl@google.com>