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.