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/news.dox

@@ -9,6 +9,24 @@
 
 @subsection features_34 New features in version 3.4
 
+@subsubsection standard_cursors_34 More standard cursors
+
+GLFW now provides the standard cursor shapes @ref GLFW_RESIZE_NWSE_CURSOR and
+@ref GLFW_RESIZE_NESW_CURSOR for diagonal resizing, @ref GLFW_RESIZE_ALL_CURSOR
+for omni-directional resizing and @ref GLFW_NOT_ALLOWED_CURSOR for showing an
+action is not allowed.
+
+Unlike the original set, these shapes may not be available everywhere and
+creation will then fail with the new @ref GLFW_CURSOR_UNAVAILABLE error.
+
+The cursors for horizontal and vertical resizing are now referred to as @ref
+GLFW_RESIZE_EW_CURSOR and @ref GLFW_RESIZE_NS_CURSOR, and the pointing hand
+cursor is now referred to as @ref GLFW_POINTING_HAND_CURSOR.  The older names
+are still available.
+
+For more information see @ref cursor_standard.
+
+
 @subsubsection features_34_win32_keymenu Support for keyboard access to Windows window menu
 
 GLFW now provides the
@@ -44,6 +62,14 @@ add_subdirectory(path/to/glfw)
 @subsubsection types_34 New types in version 3.4
 @subsubsection constants_34 New constants in version 3.4
 
+ - @ref GLFW_POINTING_HAND_CURSOR
+ - @ref GLFW_RESIZE_EW_CURSOR
+ - @ref GLFW_RESIZE_NS_CURSOR
+ - @ref GLFW_RESIZE_NWSE_CURSOR
+ - @ref GLFW_RESIZE_NESW_CURSOR
+ - @ref GLFW_RESIZE_ALL_CURSOR
+ - @ref GLFW_NOT_ALLOWED_CURSOR
+ - @ref GLFW_CURSOR_UNAVAILABLE
  - @ref GLFW_WIN32_KEYBOARD_MENU