Apply PrimarySwitchPreference to InputMethodPreference

There are 2 kinds of InputMethodPreferences for
2 keyboard settings pages:
-. Display enabled IMEs and user can tap them
   into IME settings.
-. Managed(enable/disable) installed IMEs.

Remove the isImeEnabler parameter and make the
InputMethodPreference support above functions.
So we can migrate 2 settings pages to single one.

Bug: 197705032
Test: atest SettingsLibTests:com.android.settingslib.inputmethod.InputMethodPreferenceTest
Change-Id: I445551e4112117aabd8d7a48f53c29b7ffd8bafd