LibIPC: Make IPC::encode() and ::decode() fail at compiletime when used

This would previously fail at runtime, and it would have zero indication
of what exactly went wrong.
Also adds `AK::DependentFalse<Ts...>', which is a...dependent false.

Libraries/LibIPC/Encoder.h

@@ -34,6 +34,7 @@ namespace IPC {
 template<typename T>
 bool encode(Encoder&, T&)
 {
+    static_assert(DependentFalse<T>, "Base IPC::encode() was instantiated");
     ASSERT_NOT_REACHED();
 }