Replace converters functions in favor of the From trait

[hate]

Objective

• The bevy_winit/converters.rs file contains many converter functions who's functionality could be achieved by implementing the From trait on the respective enums/structs.
• With this change, we can just call the .into() method for the aforementioned enums/structs.
• I made this PR to see if this change would be feasible, if the converter functions are preferred over the From implementations, then this PR should be closed.

Solution

Added the following trait implementations:

• impl From<winit::event::KeyboardInput> for KeyboardInput
• impl From<winit::event::VirtualKeyCode> for KeyCode
• impl From<winit::event::ElementState> for ButtonState
• impl From<winit::event::MouseButton> for MouseButton
• impl From<CursorIcon> for winit::window::CursorIcon
• impl From<WindowLevel> for winit::window::WindowLevel

To support this change, the winit crate must be added as a dependency in bevy_input and bevy_window crates.

[alice-i-cecile]

I like this better, but I remember trying this before and @mockersf complaining at me for some reason ;)

The added dependency is a bit annoying: in theory bevy_input could be agnostic to the windowing backend. It compiles though, so no immediate circular dependency. We could also feature flag this, which I think is fairly sensible.

[hate]

Right, I wasn't too sure how to feel about the added dependency either, I just figured to go through with the implementation, since it would have to get added either way if the From trait were to be used instead of a converter function here: #8593 (comment)