- Use a window method to handle updating the window after scale changes.
This avoids the need for methods that return mutable references to
DPI & scale.
- Remove window.outputs() method that returned window->system->outputs
as it is misleading to expose these as window outputs when the outpurs
returned are all known outputs.
- Use a vector instead of an unordered_set to store window outputs,
while a 'set' does make sense, it means the outputs can't be accessed
in the order they're added which may be useful for further changes.
- Use early returns.
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