Extract telephony-protos target.

After this CL, the protos that were formerly part of telephony-common
are now a separate build target. This allows telephony-protos to be
pinned to a particular java_version (in a follow-up CL), and more
generally separates the proto-related from not proto-related build
configuration.

Bug: 72703434
Test: Treehugger
Change-Id: I1c1d95e24f584b73e5fe64ca6251fa7b153fba0b