Update to the ActivityManager proto

Rename the activitymanager.proto to enums.proto, in accordance with the
new convention on naming these protos.
Also, changes processStateAmToProto from simplying multiplying by 100 to
a switch statement, to be more future-proof.
Also, changes the values of the proto's process state, to reflect that
the values will not be kept in sync with ActivityManager.

Note that this cl was originally started in ag/3008434, and partially fulfilled in ag/3114337.

Bug: 69478930
Test: run cts-dev -m CtsStatsdHostTestCases -t android.cts.statsd.ProcStateAtomTests
Change-Id: I2b3bf2552b879c74d8985338df5a57c01850cb91