Prepare to make InputMethodUtils package-private

In Bug 77730201, we cleaned up a bunch of files so that only modules
inside framework/base depend on InputMethodUtils.  This CL is a
preparation of a further hardening.

Just by moving two utility methods from InputMethodUtils to
LocaleUtils, InputMethodUtils is used only from
InputMethodManagerService and its direct dependencies.  This allows us
to make InputMethodUtils package-private class to make sure anyone
outside our team is unexpectedly depending on InputMethodUtils in a
subsequent CL.

This is a mechanical refactoring.  There should be no observable
behavior difference.

Bug: 114660660
Test: atest CtsInputMethodTestCases CtsInputMethodServiceHostTestCases
Test: atest FrameworksCoreTests:com.android.internal.inputmethod
Change-Id: Ie8cb198880a145a7b81d2bf1eae1531ac3614019