Add proto-based client side dumping for IME tracing

This CL implements a mechanism to dump IME related client states into
a proto file which can later be imported to winscope to allow easy
debugging. A new abstract class ImeTracing.java declares the methods
related to scheduling, collecting and dumping logs. Two child class
implement these methods for server and client separately.

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: Ia89f11d5ef8a220ea7746191b18769cea5a8359d