Tweak get_cursor code (#713)

Co-authored-by: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>

masonry/src/contexts.rs

@@ -368,7 +368,7 @@ impl_context_method!(
 
 // --- MARK: CURSOR ---
 // Cursor-related impls.
-impl_context_method!(EventCtx<'_>, {
+impl_context_method!(MutateCtx<'_>, EventCtx<'_>, UpdateCtx<'_>, {
     /// Notifies Masonry that the cursor returned by [`Widget::get_cursor`] has changed.
     ///
     /// This is mostly meant for cases where the cursor changes even if the pointer doesn't

masonry/src/widget/widget.rs

@@ -224,6 +224,8 @@ pub trait Widget: AsAny {
 
     /// Return the cursor icon for this widget.
     ///
+    /// This will be called when the mouse moves or [`cursor_icon_changed`](MutateCtx::cursor_icon_changed) is called.
+    ///
     /// **pos** - the mouse position in global coordinates (e.g. `(0,0)` is the top-left corner of the
     /// window).
     fn get_cursor(&self, ctx: &QueryCtx, pos: Point) -> CursorIcon {