[a11y] Fix talkback column and item count for AllAppsGrid

The new ItemCount API in Baklava is for AccessibilityNodeInfo, for total
items in grid. Since in AllApps grid we override and use
AccessbiilityNodeInfoForItem for the specific app within the column, we
should instead fix the column count override with the proper column counts.

Bug: b/228935017
Flag: EXEMPT a11y bug fix
Test: Manual; Before: https://recall.googleplex.com/clips/24b23bab-add8-4c13-a203-9f92144537a3
Test: Manual; After: https://recall.googleplex.com/clips/d9190fb5-c912-4dc9-8a09-868a1a1fd500
Test: Manual; Changing grid: http://recall/clips/2d513dc2-ffee-4680-95a0-ba263155d194
Change-Id: Id4a22fdbd258bca8102c16502629ea51971b139d