gpui: Add debug assertion to Window::on_action and make docs consistent (#41202)

Improves formatting consistency across various docs, fixes some typos,
and adds a missing `debug_assert_paint` to `Window::on_action` and
`Window::on_action_when`.

Release Notes:

- N/A

crates/gpui/src/interactive.rs

@@ -355,7 +355,7 @@ impl Default for NavigationDirection {
     }
 }
 
-/// A mouse move event from the platform
+/// A mouse move event from the platform.
 #[derive(Clone, Debug, Default)]
 pub struct MouseMoveEvent {
     /// The position of the mouse on the window.
@@ -383,7 +383,7 @@ impl MouseMoveEvent {
     }
 }
 
-/// A mouse wheel event from the platform
+/// A mouse wheel event from the platform.
 #[derive(Clone, Debug, Default)]
 pub struct ScrollWheelEvent {
     /// The position of the mouse on the window.