Prevent IMEs from switching to another IME that isn't enabled

Fixes an issue where the current IME can switch to any IME,
even if it hasn't been enabled.

Fixes: 227207653
Test: atest android.view.inputmethod.cts.InputMethodServiceTest
Change-Id: I12829de9fa58610a7d53e4b154e1550f0f791e75
1 file changed