Rust protobuf 2->3: Update Bluetooth

tldr: remove protobuf2 from Android Rust and upgrade everything to pb3.

These commits update:
- The grpcio rust crate to use protobuf 3
- The build system to always use the new libprotobuf (pb3) instead of the _deprecated variant (for pb2); they also force-enable libprotobuf everywhere, ignoring the use_protobuf3 flag, removes the tests related to pb2
- The following modules, which required syntax changes:
-- packages/modules/Bluetooth
-- device/google/cuttlefish
-- vendor/auto

Bug: 308790516
Test: m rust
Flag: EXEMPT 3p rust crate upgrade

Change-Id: I6f4589dcf503f3a360c3bc4ade7844e858ed618e