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

src/com/android/settings/CryptKeeper.java

@@ -773,9 +773,10 @@ public class CryptKeeper extends Activity implements TextView.OnEditorActionList
         if (imeSwitcher != null && hasMultipleEnabledIMEsOrSubtypes(imm, false)) {
             imeSwitcher.setVisibility(View.VISIBLE);
             imeSwitcher.setOnClickListener(new OnClickListener() {
-                    @Override
+                @Override
                 public void onClick(View v) {
-                    imm.showInputMethodPicker(false /* showAuxiliarySubtypes */);
+                    imm.showInputMethodPickerFromSystem(false /* showAuxiliarySubtypes */,
+                            v.getDisplay().getDisplayId());
                 }
             });
         }