Present target grid as hierarchical for a11y purposes.

A retrofit of the ag/31256785 into the legacy codebase (which is still
used by MediaProjection, at least).

Present target grid as hierarchical for a11y purposes. This makes
TalkBack to announce sub-groups of targets.

Fix: 380211084
Test: Manual testing for the both cases when the suggested apps are
present and missing.
Flag: android.service.chooser.announce_shortcuts_and_suggested_apps_legacy

Change-Id: Ifc13bcfacf791cea8ca4d661a847dfa9dafc950f