CursorGetTextureCallback
typealias CursorGetTextureCallback = (cursor: Cursor, <Error class: unknown class>, <Error class: unknown class>, <Error class: unknown class>?) -> Texture?
The type of callback used by a dynamic GdkCursor to generate a texture for the cursor image at the given @cursor_size and @scale.
The actual cursor size in application pixels may be different from @cursor_size x @cursor_size, and will be returned in