Add documentation comments to bevy_window (#4333)

# Objective
- Add documentation comments and `#![warn(missing_docs)]` to `bevy_window`.
- Part of #3492

crates/bevy_window/src/cursor.rs

@@ -1,39 +1,80 @@
-/// The icon to display for a window's cursor
+/// The icon to display for a window's cursor.
+///
+/// Examples of all of these cursors can be found [here](https://www.w3schools.com/cssref/playit.asp?filename=playcss_cursor).
+/// This `enum` is simply a copy of a similar `enum` found in [`winit`](https://docs.rs/winit/latest/winit/window/enum.CursorIcon.html).
+/// `winit`, in turn, mostly copied cursor types avilable in the browser.
 #[derive(Debug, Hash, PartialEq, Eq, Clone, Copy)]
 pub enum CursorIcon {
+    /// The platform-dependent default cursor.
     Default,
+    /// A simple crosshair.   
     Crosshair,
+    /// A hand (often used to indicate links in web browsers).    
     Hand,
+    /// An arrow. This is the default cursor on most systems.    
     Arrow,
+    /// Indicates something is to be moved.    
     Move,
+    /// Indicates text that may be selected or edited.    
     Text,
+    /// Program busy indicator.    
     Wait,
+    /// Help indicator (often rendered as a "?")    
     Help,
+    /// Progress indicator. Shows that processing is being done. But in contrast
+    /// with "Wait" the user may still interact with the program. Often rendered
+    /// as a spinning beach ball, or an arrow with a watch or hourglass.    
     Progress,
+    /// Cursor showing that something cannot be done.    
     NotAllowed,
+    /// Indicates that a context menu is available
     ContextMenu,
+    /// Indicates that a cell (or set of cells) may be selected
     Cell,
+    /// Indicates vertical text that may be selected or edited
     VerticalText,
+    /// Indicates that an alias of something is to be created
     Alias,
+    /// Indicates something is to be copied
     Copy,
+    /// Indicates that the dragged item cannot be dropped here
     NoDrop,
+    /// Indicates that something can be grabbed    
     Grab,
+    /// Indicates that something is grabbed.    
     Grabbing,
+    /// Indicates that the user can scroll by dragging the mouse.
     AllScroll,
+    /// Indicates that the user can zoom in
     ZoomIn,
+    /// Indicates that the user can zoom out
     ZoomOut,
+    /// Indicates that an edge of a box is to be moved right (east)
     EResize,
+    /// Indicates that an edge of a box is to be moved up (north)
     NResize,
+    /// Indicates that an edge of a box is to be moved up and right (north/east)
     NeResize,
+    /// indicates that an edge of a box is to be moved up and left (north/west)
     NwResize,
+    /// Indicates that an edge of a box is to be moved down (south)
     SResize,
+    /// The cursor indicates that an edge of a box is to be moved down and right (south/east)
     SeResize,
+    /// The cursor indicates that an edge of a box is to be moved down and left (south/west)
     SwResize,
+    /// Indicates that an edge of a box is to be moved left (west)
     WResize,
+    /// Indicates a bidirectional resize cursor
     EwResize,
+    /// Indicates a bidirectional resize cursor
     NsResize,
+    /// Indicates a bidirectional resize cursor
     NeswResize,
+    /// Indicates a bidirectional resize cursor
     NwseResize,
+    /// Indicates that a column can be resized horizontally
     ColResize,
+    /// Indicates that the row can be resized vertically
     RowResize,
 }

crates/bevy_window/src/event.rs

@@ -58,18 +58,18 @@ pub struct WindowCloseRequested {
 pub struct WindowClosed {
     pub id: WindowId,
 }
-
+/// An event that is sent whenenver the user's cursor moves.
 #[derive(Debug, Clone)]
 pub struct CursorMoved {
     pub id: WindowId,
     pub position: Vec2,
 }
-
+/// An event that is sent whenever the user's cursor enters a window.
 #[derive(Debug, Clone)]
 pub struct CursorEntered {
     pub id: WindowId,
 }
-
+/// An event that is sent whenever the user's cursor leaves a window.
 #[derive(Debug, Clone)]
 pub struct CursorLeft {
     pub id: WindowId,

crates/bevy_window/src/lib.rs

@@ -1,3 +1,4 @@
+#[warn(missing_docs)]
 mod cursor;
 mod event;
 mod raw_window_handle;
@@ -23,6 +24,7 @@ pub mod prelude {
 use bevy_app::prelude::*;
 use bevy_ecs::{event::Events, schedule::SystemLabel};
 
+/// A [`Plugin`] that defines an interface for windowing support in Bevy.
 pub struct WindowPlugin {
     /// Whether to create a window when added.
     ///