UI: Capabilities Flag for Clipboard Image copy/paste

This adds an WM_capabilities_flag to indicate that a platform
implements support for copying and pasting images using a shared
clipboard.

Pull Request: https://projects.blender.org/blender/blender/pulls/106990

source/blender/windowmanager/WM_api.h

@@ -138,6 +138,8 @@ typedef enum eWM_CapabilitiesFlag {
    * Reading from the back-buffer is supported.
    */
   WM_CAPABILITY_GPU_FRONT_BUFFER_READ = (1 << 3),
+  /** Ability to copy/paste system clipboard images. */
+  WM_CAPABILITY_CLIPBOARD_IMAGES = (1 << 4),
 } eWM_CapabilitiesFlag;
 
 eWM_CapabilitiesFlag WM_capabilities_flag(void);

source/blender/windowmanager/intern/wm_window.c

@@ -1852,6 +1852,9 @@ eWM_CapabilitiesFlag WM_capabilities_flag(void)
   if (ghost_flag & GHOST_kCapabilityGPUReadFrontBuffer) {
     flag |= WM_CAPABILITY_GPU_FRONT_BUFFER_READ;
   }
+  if (ghost_flag & GHOST_kCapabilityClipboardImages) {
+    flag |= WM_CAPABILITY_CLIPBOARD_IMAGES;
+  }
 
   return flag;
 }