Populates collection info count for A11y toggle feature pages.

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