tmux: Paste primary selection with middle mouse

Similar to everywhere else, paste the primary X selection (XA_PRIMARY)
instead of the most recent tmux paste buffer.

TODO: Forward event to 'root' key-table to prevent code duplication

.config/tmux/tmux.conf

@@ -69,6 +69,25 @@ bind -n TripleClick1Pane {
 	}
 }
 
+# Paste primary selection with middle mouse button
+bind -n MouseDown2Pane {
+	select-pane -t=
+	if -F "#{||:#{pane_in_mode},#{mouse_any_flag}}" {
+		send -M
+	} {
+		run 'tmux set-buffer -b XA_PRIMARY "$(xclip -selection p -o)"'
+		paste-buffer -p -b XA_PRIMARY
+	}
+}
+# When in copy-mode do the same but leave copy-mode first
+bind -T copy-mode-vi MouseDown2Pane {
+	select-pane -t=
+	send -X cancel
+	# TODO: Forward click to 'root' key-table to prevent code duplication
+	run 'tmux set-buffer -b XA_PRIMARY "$(xclip -selection p -o)"'
+	paste-buffer -p -b XA_PRIMARY
+}
+
 # Scroll up 5 lines when entering copy-mode through the mouse wheel, send 5x`up`
 # when the current pane is in alternate mode and discard the `-e` flag passed to
 # copy-mode from the default binding (See below)