add ghost function getAllDisplayDimensions, GHOST_GetAllDisplayDimensions

This returns the desktop size, not just the size of the active monitor, useful since this constrains the mouse and we dont have to detect the active monitor (which isn't so straightforward with xlib).

carbon/cocoa are TODO, they still use getMainDisplayDimensions().

intern/ghost/GHOST_C-api.h

@@ -148,6 +148,20 @@ extern void GHOST_GetMainDisplayDimensions(GHOST_SystemHandle systemhandle,
                                            GHOST_TUns32 *width,
                                            GHOST_TUns32 *height);
 
+/**
+ * Returns the dimensions of all displays combine
+ * (the current workspace).
+ * No need to worrky about overlapping monitors.
+ * \param systemhandle The handle to the system
+ * \param width A pointer the width gets put in
+ * \param height A pointer the height gets put in
+ * \return void.
+ */
+extern void GHOST_GetAllDisplayDimensions(GHOST_SystemHandle systemhandle,
+                                           GHOST_TUns32 *width,
+                                           GHOST_TUns32 *height);
+
+
 /**
  * Create a new window.
  * The new window is added to the list of windows managed.