ProtoLog: Better behavior when parsing fails

Improves behavior when parsing fails; now, ProtoLog skips the offending files, and
relies on the subsequent compilation step to catch the error.

Additionally, the build no longer fails when the canonical protolog.json file contains
obsolete entries.

Test: Introduce syntax error in services/core/ file, make and verify error messaging is sound
Change-Id: Ic23dec4a14489316ecb0e46bbabe246ddae29655