Custom pointer icons

[Adanos020]

Is your feature request related to a problem? Please describe.
I would like my game editor application to be able to change the mouse cursor icon to a custom image. I'm sure many other kinds of applications like image manipulation software could also benefit from this feature

Describe the solution you'd like
The ideal solution would be to just add an extra Custom(ColorImage) or Custom(TextureId) variant to the CursorIcon enum. Please let me know which one is better!

Describe alternatives you've considered
If the above solution isn't viable, another decent one seems to be adding a set_custom_cursor_icon method to Context.

Additional context
Here's an example of what I want to achieve:

Also, we're waiting for winit to release with the recently merged PR that added this feature which we can then use in eframe.

[timmb]

This would be really helpful for us as well - even if it was just an identifier like Custom(&'static str) as we're ultimately using CSS to draw the cursor.