Move current subtype management code to RichInputMethodManager

...method/latin/settings/AdditionalFeaturesSettingUtils.java

...rc/com/android/inputmethod/keyboard/KeyboardSwitcher.java

java/src/com/android/inputmethod/latin/LatinIME.java

...com/android/inputmethod/latin/RichInputMethodManager.java

java/src/com/android/inputmethod/latin/SubtypeSwitcher.java

tests/src/com/android/inputmethod/latin/InputTestsBase.java