MetaCursorSprite: Put renderer specific code in the renderer

There were lots of code handling the native renderer specific cases;
move these parts to the renderer. Note that this causes the X11 case to
always generate the texture which is a waste of memory, but his
regression will be fixed in a following commit.

The lazy loading of the texture was removed because it was eventually
always loaded anyway indirectly by the renderer to calculate the
current rect.

https://bugzilla.gnome.org/show_bug.cgi?id=744932