Change `run_app(app: &mut A)` to `run_app(app: A)`

[madsmtm]

Since https://github.com/rust-windowing/winit/pull/3709, we do a blanket impl of ApplicationHandler for &mut references. This means that we can now change run_app_x methods to consume the application instead of taking a reference to it.

This allows the user more control over how they pass their application state to Winit.

Internally, each backend is free to convert the app to an &mut app (or &mut dyn ApplicationHandler) if that's easier for them to pass around.

• [ ] Tested on all platforms changed
• [x] Added an entry to the changelog module if knowledge of this change could be valuable to users