Avoid IME restart for configChanges

Handle onConfigurationChanged() in order to prevent restarting
InputMethodService everytime. We introduce a new API attribute
"configChanges" in InputMethod(attrs.xml) which when declared
by IME, will be responsible for handling mentioned
configuration changes.

This CL re-introduces [1] with fix: Use new Configuration instance for
IMS#mLastKnownConfig

[1] Iff88b768c6b06cf5cf1fe9e97ee97f8f78e6f0bd

Bug: 167948419
Test: atest InputMethodServiceTest
    Manually:
      1. Patch Ie91e7a8e06b80864ef9409031e8543858552d70d to use dual
         display area.
      2. Open applications with editors on both display areas.
      3. Attach a debug point for IMS#onConfigurationChanged().
      4. Make sure IMS#resetStateForNewConfiguration() is not called
         when IME moves between these two identical DisplayAreas

Change-Id: Ib94fddadb0dae648cf73a4c1642e51edebd19f50