Use LocaleList for implicitly enabled subtypes.

There are two major changes in this CL:

  1. Now IMMS resets its internal state whenever the system locale list
     is changed, rather than just checking the primary system locale.
  2. For software keyboard subtypes,
     InputMethodUtils#getImplicitlyApplicableSubtypesLocked() now takes
     the entire system locale list into account when determining what
     subtypes should be enabled by default when the user does not
     explicitly enable one or more subtypes.

Bug: 27129703
Change-Id: Iaf179d60c12b9a98b4f097e2449471c4184e049b