system/dbus: buffer xdg-dbus-proxy messages

Pointing xdg-dbus-proxy to stdout/stderr makes a huge mess. This change enables app to neatly print out prefixed xdg-dbus-proxy messages after output is resumed.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

internal/app/seal.go

@@ -41,6 +41,8 @@ type appSeal struct {
 	id string
 	// wayland mediation, disabled if nil
 	wl *shim.Wayland
+	// dbus proxy message buffer retriever
+	dbusMsg func(f func(msgbuf []string))
 
 	// freedesktop application ID
 	fid string