Expose isSystemImeThatHasSubtypeOf to Settings

This is a follow up CL for a recent attempt to minimize
the number of default enabled IMEs.
- part1: I831502db502f4073c9c2f50ce7705a4e45e2e1e3
- part2: Ife93d909fb8a24471c425c903e2b7048826e17a3
- part3: I6571d464a46453934f0a8f5e79018a67a9a3c845
- part4: I871ccda787eb0f1099ba3574356c1da4b33681f3

In the avobe CLs, an internal (hidden) method
InputMethodUtils.isValidSystemDefaultIme was marked as
deprecated and we decided to migrate to
InputMethodUtils.isSystemImeThatHasSubtypeOf.

To finish this refactoring, this CL make the new
method visible to the settings app.

InputMethodUtils.isValidSystemDefaultIme remains
to be an internal method. No behavior change is
intended.

Change-Id: I8cb9ca40d15af099c3d1ded46797fb57f14fb9e8