Rust protobuf 2->3: Update build system

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
Ignore-AOSP-First: must be done in main to upgrade cuttlefish+vendor with the rest all at once
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:7d0783ce22b3d7d369786d4b16067c79c033185b)
Merged-In: I1d07c433aca41ccfe2e710821cf930c413dc12d6

Change-Id: I1d07c433aca41ccfe2e710821cf930c413dc12d6