Optimized workflow for IME tracing on clients side

Optimized the tracing logic for the IME clients information. The
clients trigger a tracing dump through the new method triggerClientDump
exposed by the ImeTracing interface. This change was done
to be able to support custom dump for clients information and
custom dump from IMS.

This change only covers the clients information. The IMS and IMMS
information will be dumped in next 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_clients.pb ime_trace_clients.pb"
Change-Id: I499cb5f45a3e78912b09b9c6cedf1ce5443e797a