Add more standard cursors

This adds the standard cursors for diagonal and omnidirectional
resize/move and operation-not-allowed.  It also adds new (better?) names
for the horizontal and vertical resize/move and pointing hand cursors.

References:
 - https://developer.apple.com/documentation/appkit/nscursor
 - https://stackoverflow.com/questions/10733228/
 - https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-setsystemcursor
 - https://freedesktop.org/wiki/Specifications/cursor-spec/
 - https://tronche.com/gui/x/xlib/appendix/b/

Related to #427.

docs/input.dox

@@ -373,12 +373,15 @@ A cursor with a [standard shape](@ref shapes) from the current system cursor
 theme can be can be created with @ref glfwCreateStandardCursor.
 
 @code
-GLFWcursor* cursor = glfwCreateStandardCursor(GLFW_HRESIZE_CURSOR);
+GLFWcursor* url_cursor = glfwCreateStandardCursor(GLFW_POINTING_HAND_CURSOR);
 @endcode
 
 These cursor objects behave in the exact same way as those created with @ref
 glfwCreateCursor except that the system cursor theme provides the actual image.
 
+A few of these shapes are not available everywhere.  If a shape is unavailable,
+`NULL` is returned.  See @ref glfwCreateStandardCursor for details.
+
 
 @subsubsection cursor_destruction Cursor destruction