This helps an accessibility service like TalkBack inform the user that
there are items that are skipped when navigating the list because they
are unimportant to accessibility.
Bug: 318607873
Test: atest AccessibilityFragmentUtilsTest
Test: atest ToggleScreenMagnificationPreferenceFragmentTest
Test: Enable TalkBack that supports the collection info count feature,
open any of the pages from the bug, observe the item count and
(un)important count are correct.
Flag: com.android.settings.accessibility.toggle_feature_fragment_collection_info
Change-Id: If64c89f2eb2f8301076baa79b9530124c850d2fc
