* Upgrade to new protobuf-codegen; use its standard
default output without local change.
* Allow a sourceProvider to have multiple output files.
For a stem.proto file, output stem.rs and mod_stem.rs.
* New protobuf-codegen option gen_mod_rs always generates
output file named "mod.rs". To generate multiple .proto
files into the same output directory, we need to rename
mod.rs to mod_<stem>.rs.
* Instead of using the gen_mod_rs option and renaming mod.rs
to mod_<stem>.rs, we generate the same mod_<stem>.rs
directly with a simple printf command.
Bug: 170256643
Test: atest -c --host --include-subdirs external/crosvm
Change-Id: Ia09e41029099a6de4d35c96dbabd9ba5514c9019