Add Windowed Mode to Gamescope Options

[MuraPura]

Adds a windowed mode to the upscaling options. Useful for really old games that open in a very tiny window due to low resolution.

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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 ✍️ ✅

[MuraPura]

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

[arielj]

Shouldn't this configuration be used to add some flag for gamescope like it's done for the other options? https://github.com/Heroic-Games-Launcher/HeroicGamesLauncher/blob/main/src/backend/launcher.ts#L200

or Windowed means no flag is passed? (I see that we currently pass either -f or -b but we have no option to not add one of those flags)

[MuraPura]

Gamescope by default is windowed. -f and -b are flags passed to change that default behavior. To my knowledge there isn't an explicit flag to pass for windowed since that is the default to begin with.