Improve latency of IME tracing

Improve latency of IME tracing by increasing the priority of the
tracing thread and adding the dump of the debugging information
at the beginning of the execution queue.

The Design Doc for IME tracing is found here: 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: I153ccac6d8b93f86f3180b0a23240c6a63758ed6