Only the text editor supported the primary clipboard & only for modal
selection. Now selecting text in the console & 3D text editing also
sets the primary clipboard under X11 & Wayland.
Notes:
- Pasting from the primary clipboard isn't yet exposed in the key-map
so in practice it's only useful for pasting text outside of Blender.
- Use skip-save option when pasting from the primary selection
so this is never used by the regular paste shortcut.
- This commit adds a primary-clipboard flag to WM_capabilities_flag() so
creating the the copy-buffer is only performed when necessary.
3dcd4df70c