Add a .pbtxt to .pb auto converter

Add a host tool which automatically convert human-readable protobuf
configurations (.pbtxt) to serialized binaries (.pb) in build-time.

Bug: 145176964
Test: atest resolv_gold_test pass
Test: mts-tradefed run -m resolv_gold_test pass

Merged-In: I45723669f82aa2f3a9a4eed0f566e1d81963d001
Change-Id: I27b68d26e331f89fa4fb8d8c9a3180b04c8c9b2c
(cherry picked from commit c944c686)