Try alternative cursor icon names

[Friz64]

Try the standardized cursor icon name, followed by a list of alternative cursor icon names (provided through rust-windowing/cursor-icon#11).

See also:

• Cursor Icon Regression on GNOME #425
• Add alternative names for cursor icons rust-windowing/cursor-icon#11

cc @kchibisov

Fixes #425

[Friz64]

Testing with the themed-window example on my machine, it now almost works perfectly, except for a few cursor icons that are still missing in my theme. For example, setting the vertical-text cursor still returns CursorNotFound. In this case, it might be beneficial to display a horizontal text cursor as a best effort. Assuming this is to be implemented, would handling this be the job of Smithay's Client Toolkit or would this behaviour be implemented in (e.g.) winit?

[kchibisov]

it now almost works perfectly, except for a few cursor icons that are still missing in my theme.

Not our issue. fix your theme, as I said. The cursor which should be used in such case is the one active at the moment, it's consistent with gtk, etc iirc.