Add proto2 files for dump of server-side IME classes

This CL adds proto2 files which declare the structure of IME related
server states dumps. These files are compiled into individual classes
which contain a fieldId for every field to be saved in the proto
dump file.

The Desing Doc for the IME tracing project is: go/ime-tracing

Bug: 154348613
Test: make and flash to see compiled classes
Change-Id: I673fb71d96ba5de2e8946f160d47ffe82198baa4