GD-541: Settings dialogue reserves way more horizontal space than it needs, leading to huge scrollbars

[mathrick]

Describe What
Currently the settings dialogue uses a very crude estimation of what horizontal space labels need, and also has custom_minimum_size hardcoded in the scene. This makes it so that it requests a lot more space than it actually needs from the scrolling container, and that makes huge scrollbars show up unnecessarily. It also makes the components wider than they need to be, so the user has to scroll a lot.

Describe Why
It's not great UI if the user has to scroll to see things.

[MikeSchulze]

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