Support selecting widget with TalkBack in edit mode

Set a11y semantics on the WidgetContent composable to enable focusing
and tapping to select widget. Widget label is announced when focused.
Since the widget and its descendants are non-interactive in edit mode,
setting a11y importance on the AndroidView will not set
:accessibilityFocus on the node in the a11y node tree.

Additionally, ignore a11y semantics of the HighlightedItem so the
widget configurator icon remains tappable.

Bug: b/337251820
Test: manual with TalkBack
Flag: ACONFIG com.android.systemui.communal_hub TEAMFOOD
Change-Id: I742926b13926287a203d1610a3567945f2f72596