Rename Window to GLRenderer

[ephemer]

Motivation

Window is a confusing name for an internal type when we already have the public UIWindow. I'm refactoring this code with the aim of implementing UIViewController in the next step (upcoming PR).

Testing Details

Builds and tests run

Please check if the PR fulfills these requirements

• [x] Self-review: I am confident this is the simplest and clearest way to achieve the expected behaviour
• [x] There are no dependencies on other PRs or I have linked dependencies through Zenhub
• [x] The commit messages are clean and understandable
• [x] Tests for the changes have been added (for bug fixes / features)
• [x] Code runs on all relevant platforms (if major change: screenshots attached)

[rikner]

@ephemer Größe oder Scale scheint irgendwie noch nicht hinzuhauen?

edit: im view controller PR funktioniert es schon wieder, weil wir dort für UIScreen.main

let size = SDL.glRenderer?.size ?? CGSize(width: 1024, height: 768)

return UIScreen(
    bounds: CGRect(origin: .zero, size: size),
    scale: SDL.glRenderer?.scale ?? 2.0 
)

verwenden. Sollten wir hier auch noch machen, damit der master sauber bleibt.

[ephemer]

@rikner it's fixed. Well spotted with the bug- thanks for reviewing!