app: move wayland mediation to shim package

Values used in the Wayland mediation implementation is stored in various struct fields strewn across multiple app structs and checks are messy and confusing. This commit unifies them into a single struct and access it using much better looking methods.

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

internal/app/app.go

@@ -1,7 +1,6 @@
 package app
 
 import (
-	"net"
 	"os/exec"
 	"sync"
 )
@@ -27,9 +26,6 @@ type app struct {
 	cmd *exec.Cmd
 	// child process related information
 	seal *appSeal
-
-	// wayland connection if wayland mediation is enabled
-	wayland *net.UnixConn
 	// error returned waiting for process
 	waitErr error