Record `Activity Center` navigation in section history and restore it on Back.
Add peek support to inspect the next history token without consuming it.
Closes#20521
This commit implements back navigation on 3 levels:
- popups will close on back (already handled by qt)
OR
- sections will swipe back from right panels to left panels (handled generally in the portrait layout)
OR
- the app will move to the previous panel in history (handled in appMain)
OR
- app will be minimised (handled in appMain)
window.onClose will not prevent app close anymore.
nimble.paths