Optimized workflow for IME tracing on InputMethodManagerService side

Optimized the tracing logic for the IMMS information. The
InputMethodManagerService triggers a tracing dump through the new
method triggerManagerServiceDump, exposed by the ImeTracing
interface.

This change only covers the IMMS information. The clients and
IMS information were added on previous changes.

Bug: 154348613
Test: start IME tracing by calling "adb shell ime tracing start"
      end IME tracing by calling "adb shell ime tracing stop"
      pull trace using "adb pull /data/misc/wmtrace/ime_trace_managerservice.pb ime_trace_managerservice.pb"
Change-Id: Ia5fb8f47769ec8c6a1a24c18cd19952c0c550274