Added new Gamescope toggle: Enable Force Grab Cursor

[RuffledPlume]

This PR is to add a QOL toggle that I've been using locally for awhile on multiple devices, it seems to be a common enough issue that a toggle would save people looking up the CLI arg and add it to the additional options.

Appends --force-grab-cursor to gamescope launch command, enabling will force the use of relative mouse mode at all times instead of flipping depending on cursor visibility. In games which flip visibility often can leave the mouse in the wrong mode, which will eventually cause the window to lose focus once the mouse escapes its bounds.

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Use the following Checklist if you have changed something on the Backend or Frontend:

• Tested the feature and it's working on a current and clean install.
• Tested the main App features and they are still working on a current and clean install. (Login, Install, Play, Uninstall, Move games, etc.)
• Created / Updated Tests (If necessary)
• Created / Updated documentation (If necessary)

[flavioislima]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[RuffledPlume]

I have read the CLA Document and I hereby sign the CLA