Improve package visibility gap for TextServicesManager

Two APIs in TextServicesManager expose the installed spell checker
packages to the caller without holding the query package permission.
  - getSpellCheckerService
  - getEnabledSpellCheckers

This cl filter the access to spell checkers from the caller by rules
of package visibilty.

Bug: 212287294
Bug: 212287061
Test: atest CtsAppEnumerationTestCases
Test: atest android.view.inputmethod.cts.SpellCheckerTest
Change-Id: I109231ca438db3a1df95a54322548bb11c026a78