Was a bit confused why the max_size API isn't exposed on `Window`, when
it's perfectly functional in `Resize`. Anyway here's the main thing that
it affects:
```rs
let screen = ctx.available_rect();
let size = screen.size();
egui::Window::new(self.name())
.resizable(true)
.resize(|resize| resize.max_size(size)) // Before
.max_size(size) // After
.show(ctx, |ui| todo!());
```
I also added some other relevant helpers for consistency.
This PR doesn't change any logic, only forwards along some helper
functions that are already public for consistency.
4886c8c8c0