[Flexiglass] Auto-focus notification shade to improve key navigation

This CL ensures that the notification shade overlay's content column
gets focus without user interaction when it appears. With this change,
the user needs only one tab to focus on the overlay's contents.

A new `clickableWithoutFocus` modifier was also created and applied
to the ShadeHighlightChip's row, allowing it to be clickable without
disrupting the focus order.

Bug: 443141191
Flag: com.android.systemui.scene_container
Change-Id: I7b1ddd4d42adf7558b8c681d95f4dfa78c05a91a