[popover] Move focus to popover content on Tab from target

[web-padawan]

Describe your motivation

Emulate the popover being next in the tab order after the target, as it will be once we refactor to native popovers:

Describe the solution you'd like

1. On target Tab, move focus to the popover overlay part (first focusable)
2. On Shift + Tab on the next focusable after the popover target, move focus back to the last popover content focusable (can be the overlay part if there are no other focusable children)
3. On Shift + Tab on the overlay part (first focusable) move focus back to the target
4. On Tab on the last popover content focusable, move focus to the next focusable after the target
5. On Tab on the body element before the popover overlay, make the focus skip the overlay