feat(A11yFeedback): Add feedback entry for downloaded Accessibility

This entry point allows users to access in the action bar.
Visibility is controlled by the aconfig and FeedbackManager#isAvailable

Bug: 393980229
Test: Manual testing on Pixel and non-Pixel devices
Test: atest ToggleFeaturePreferenceFragmentTest
Flag: com.android.server.accessibility.enable_low_vision_generic_feedback
Change-Id: Ie6dfb6a887fe5a894622e86bab39878f8adea758