sway sends wl_keyboard.enter on seat focus change and when a keyboard
active on a seat is configured. If all keyboards are removed and a
keyboard is added back without changing the focused client, no new
notify event would be sent despite having keyboard focus. This could
lead to key events without notify, which is a protocol violation.
As a quick fix, when configuring a keyboard on a seat where no keyboard
is currently active, activate the keyboard so that a focused surface
will receive a notify event.
Regressed by: e1b268af98
Closes: https://github.com/swaywm/sway/issues/7330
(cherry picked from commit 1ade0ce753)
6b900bab60