Add proto-based InputMethodService and server side dumping for IME

This CL implements a mechanism to dump InputMethodService and IME
related server states into a proto file which can later be imported
to Winscope to allow easy debugging.

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

Bug: 154348613
Test: start trace by calling "adb shell ime tracing start"
      end trace by calling "adb shell ime tracing stop"
      pull trace using "adb pull /data/misc/wmtrace/ime_trace.pb ime_trace.pb"
Change-Id: Icbfb8c11e882f29eb45dea9d4c23315c48e9d619