Add a sample multi-client IME

This CL adds a sample multi-client IME.  Ahthough there are still many
limitations and missing features in this sample IME, this CL
demonstrates how a multi-client IME can be implemented.

Fix: 115784148
Test: prebuilts/checkstyle/checkstyle.py -f \
      development/samples/MultiClientInputMethod/
Test: Manually verified as follows:
  1. make -j MultiClientInputMethod
  2. adb install -r $OUT/system/priv-app/MultiClientInputMethod/MultiClientInputMethod.apk
  3. adb root
  4. adb shell setprop persist.debug.multi_client_ime \
       com.example.android.multiclientinputmethod/.MultiClientInputMethod
  5. adb reboot
  6. Try multiple text input scenario
Change-Id: Ide43e16448fa00355a2c08bc45ae94d98553da50
17 files changed