Windows as Entities (#5589)

# Objective

Fix bevyengine/bevy#4530

- Make it easier to open/close/modify windows by setting them up as `Entity`s with a `Window` component.
- Make multiple windows very simple to set up. (just add a `Window` component to an entity and it should open)

## Solution

- Move all properties of window descriptor to ~components~ a component.
- Replace `WindowId` with `Entity`.
- ~Use change detection for components to update backend rather than events/commands. (The `CursorMoved`/`WindowResized`/... events are kept for user convenience.~
  Check each field individually to see what we need to update, events are still kept for user convenience.

---

## Changelog

- `WindowDescriptor` renamed to `Window`.
    - Width/height consolidated into a `WindowResolution` component.
    - Requesting maximization/minimization is done on the [`Window::state`] field.
- `WindowId` is now `Entity`.

## Migration Guide

- Replace `WindowDescriptor` with `Window`.
    - Change `width` and `height` fields in a `WindowResolution`, either by doing
      ```rust
      WindowResolution::new(width, height) // Explicitly
      // or using From<_> for tuples for convenience
      (1920., 1080.).into()
      ```
- Replace any `WindowCommand` code to just modify the `Window`'s fields directly  and creating/closing windows is now by spawning/despawning an entity with a `Window` component like so:
  ```rust
  let window = commands.spawn(Window { ... }).id(); // open window
  commands.entity(window).despawn(); // close window
  ```

## Unresolved
- ~How do we tell when a window is minimized by a user?~
  ~Currently using the `Resize(0, 0)` as an indicator of minimization.~
  No longer attempting to tell given how finnicky this was across platforms, now the user can only request that a window be maximized/minimized.
  
 ## Future work
 - Move `exit_on_close` functionality out from windowing and into app(?)
 - bevyengine/bevy#5621
 - bevyengine/bevy#7099
 - bevyengine/bevy#7098


Co-authored-by: Carter Anderson <[email protected]>

Author: Aceeri

src/converters.rs

@@ -33,7 +33,7 @@ pub fn convert_mouse_button(mouse_button: winit::event::MouseButton) -> MouseBut
 
 pub fn convert_touch_input(
     touch_input: winit::event::Touch,
-    location: winit::dpi::LogicalPosition<f32>,
+    location: winit::dpi::LogicalPosition<f64>,
 ) -> TouchInput {
     TouchInput {
         phase: match touch_input.phase {
@@ -42,7 +42,7 @@ pub fn convert_touch_input(
             winit::event::TouchPhase::Ended => TouchPhase::Ended,
             winit::event::TouchPhase::Cancelled => TouchPhase::Cancelled,
         },
-        position: Vec2::new(location.x, location.y),
+        position: Vec2::new(location.x as f32, location.y as f32),
         force: touch_input.force.map(|f| match f {
             winit::event::Force::Calibrated {
                 force,