Remove custom focus logic

Using the system logic for focus handling so that partially visible contents are
properly handled, eg in overview only hotseat is visible
This does changes the focus logic on workspace when both icons and widgets or different sizes
are present, we may consider reviving (parts of) this logic in the future

Bug: 80189843
Change-Id: I874e284e0a62b579c24d36db9b74da3de7a7e367