[binder_rs] Make Binder interfaces and Strong<> Sync

NDK Binder objects are thread-safe, so our Rust interfaces and Strong<>
objects can be marked as Sync.

Test: atest -p frameworks/native/libs/binder --include-subdirs
Bug: 164453341
Change-Id: I9aea4413cae14af136e1d6f5f4143cce30d65a37
3 files changed