Also make SELECTED_INPUT_METHOD_SUBTYPE per-profile

This is a follow up CL to my previous CL [1], which implemented
per-profile IME behind the flag.

Some secure settings need to be cloned to the profile owner's settings
depending on whether per-profile IME is enabled or not.  My previous
CL correctly took care of the following settings,
 * DEFAULT_INPUT_METHOD
 * ENABLED_INPUT_METHODS
 * SELECTED_SPELL_CHECKER
 * SELECTED_SPELL_CHECKER_SUBTYPE
but somehow forgot to do so for SELECTED_INPUT_METHOD_SUBTYPE.

With this CL, SELECTED_INPUT_METHOD_SUBTYPE also becomes per-profile
when per-profile IME is enabled with the runtime flag.

 [1]: Ied99664d3dc61b97c919b220c601f90b29761b96
      a878b950

Bug: 121348796
Test: Manually made sure as follows.
  1. adb root
  2. adb shell setprop persist.debug.per_profile_ime 1
  3. adb reboot
  4. Install Test DPC.
  5. Enable managed profile with Test DPC.
  6. adb shell settings 'put secure --user 0 enabled_input_methods \
      "com.android.inputmethod.latin/.LatinIME;-921088104;774684257"'
  7. adb shell settings 'put secure --user 10 enabled_input_methods \
      "com.android.inputmethod.latin/.LatinIME;-921088104;774684257"'
  8. Open "Files" app for the main profile.
  9. Tap the search box to show AOSP Keyboard.
 10. Tap the globe button on the AOSP Keyboard to switch to Deutsch
     layout.
 11. Open "Files" app for the work profile.
 12. Tap the search box to show AOSP Keyboard.
 13. Make sure that the AOSP Keyboard is in English layout.
Change-Id: I9696396eb5f99b2e45a95d356b4da09502ac7e3d