Qt: add fullscreen mouse lock setting

[ibancel]

Add a mouse lock setting in order to control the lock state when entering in fullscreen mode.
It can be useful when having multiple monitors.

[Megamouse]

I don't know if this setting is actually necessary.
You can already set and release the lock with Ctrl+L

It would only serve as a pure setting that does not default to locked when entering fullscreen.
Unless that is what you wanted.

[ibancel]

I don't know if this setting is actually necessary.
You can already set and release the lock with Ctrl+L

It would only serve as a pure setting that does not default to locked when entering fullscreen.
Unless that is what you wanted.

Yes it is only for defaulting when entering in fullscreen. This is bothering to do Ctrl+L each time and the shortcut is not obvious for newcomers in my opinion.

[Megamouse]

I could imagine that the more annoying part might be that - once you escaped it - you again get trapped as soon as you enter the game's monitor with your mouse.

[Megamouse]

I searched for possible loopholes with the lock state but the code seems sound to me 👍
We'll now once someone complains.