Fix focus navigation of All Apps when using external keyboard.

- All apps icons do not show the focus rectangle when focused as mIconFocusListener is null in BaseAllAppsAdapter when onCreateViewHolder is called.
- All apps recyclerview does not scroll down when focus goes from top to bottom of list, as AllAppsToastUiDelegate calls hideKeyboard which clears focus.
- Focus goes behind AllApps into hotseat, so update hotseat setDescendantFocusability.

Flag: NONE
Fix: 296844600
Test: TaplKeyboardFocusTest
Change-Id: I65f6fbb6f4df0be4b4ff922dda267d27da16effe