Replace libxcursor with custom cursor code

[notgull]

Another one bites the dust.

This replaces the code dependent on libxcursor with equivalent code written using x11rb, featuring its special "cursor" module.

cc #3198

• [x] Tested on all platforms changed
• [x] Added an entry to the changelog module if knowledge of this change could be valuable to users
• [x] Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• [x] Created or updated an example program if it would help users understand this functionality
• [x] Updated feature matrix, if new features were added or implemented

[madsmtm]

Meeting resolution: @kchibisov will take a look once he has time