IMM#showInputMethodPickerFromSystem for supporting multi-display.

Derived from IMM#showInputMethodPicker(bool) @hide function, rename it as
showInputMethodPickerFromSystem and added displayId parameter to let
system caller can deside which display to show input method picker dialog.

Bug: 120050928
Test: manual, verify the IME switcher dialog can be shown on the external
      display when:
      1) Launch CryptKeeper activity to the external display via command:
   adb shell am start -e "com.android.settings.CryptKeeper.DEBUG_FORCE_VIEW" \
   "password" -n com.android.settings/.CryptKeeper --display 1 --windowingMode 1
      2) Pressing the IME switcher button in CryptKeeper activity.
Test: atest InputMethodManagerTest#testShowInputMethodPicker

Change-Id: I58f4e7b00eb271d426ba5b1125e9f129dac53f1d