m: Replace libxcursor with custom cursor code

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

Signed-off-by: John Nunley <dev@notgull.net>

src/platform_impl/linux/x11/mod.rs

@@ -906,6 +906,9 @@ pub enum X11Error {
 
     /// Failed to get property.
     GetProperty(util::GetPropertyError),
+
+    /// Could not find an ARGB32 pict format.
+    NoArgb32Format,
 }
 
 impl fmt::Display for X11Error {
@@ -930,6 +933,9 @@ impl fmt::Display for X11Error {
             X11Error::XsettingsParse(err) => {
                 write!(f, "Failed to parse xsettings: {:?}", err)
             },
+            X11Error::NoArgb32Format => {
+                f.write_str("winit only supports X11 displays with ARGB32 picture formats")
+            },
         }
     }
 }