ANDROID: rust_binder: add process freezing

When you want to freeze a process, you should process all incoming
transactions before you freeze it. This patch helps with that. The idea
is that before you freeze the process, you mark it as frozen in the
binder driver. When this happens, all new incoming transactions are
rejected, which lets you empty the queue of incoming transactions that
were sent before you decided to freeze the process. Once you have
processed every transaction in that queue, you can perform the actual
freeze operation.

Link: https://lore.kernel.org/rust-for-linux/20231101-rust-binder-v1-15-08ba9197f637@google.com/


Change-Id: Iae79352b897618913a0c710596da98e9f274c58b
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Bug: 278052745