Add proto dumpstate mode

Add a "PROTO" dumpstate mode to request a protobuf dump from
IDumpstateDevice HAL, primarily used by incidentd to get
device-specific state as a proto for automated issue reporting and
debugging.
Since the format of these states can vary across vendors and devices,
the proto schema will not be defined in AOSP.

Bug: 140521164
Test: VtsHalDumpstateV1_1TargetTest
Change-Id: I1d586c99b654471db5028039792c3d9e6e2184bb
Merged-In: I1d586c99b654471db5028039792c3d9e6e2184bb