Launch AOSP Keyboard Settings on the same display

This CL demonstrates how an IME can show an Activity on the display
where the IME is shown.  The key points are:

 * The current display ID can be obtained as follows.

    final int curentDisplayId = inputMethodService
            .getSystemService(WindowManager.class)
            .getDefaultDisplay()
            .getDisplayId();

 * When launching an Activity, specify the target display ID as
   follows.

    inputMethodService.startActivity(intent, ActivityOptions
            .makeBasic()
            .setLaunchDisplayId(curentDisplayId)
            .toBundle());

Fix: 131718879
Test: Manually verified as follows.
  1. Build aosp_blueline-userdebug and flash it.
  2. adb shell settings put global force_desktop_mode_on_external_displays 1
  3. adb shell settings put global overlay_display_devices 1920x1080/320
  4. adb reboot
  5. With a mouse, launch any application that has input field
     in the secondary display.
  6. Click that input field to bring up AOSP Keyboard.
  7. Long click the comma key then select the gear icon.
  8. Select "Android Keyboard Settings (AOSP)"
  9. Make sure that the AOSP Keyboard Settings is launched in
     the secondary display, not in the default display.
 10. Go back to the step 7.
 11. Select "Languages"
 12. Subtype Enabler for AOSP Keyboard is shown in the secondary
     display, not in the default display.
Change-Id: I9f89f371c38d9a7b5a06d018d4b41aa09815ea24