LibIPC+Everywhere: Always pass ownership of transferred data to clients

This has been a longstanding ergonomic issue with our IPC compiler. Non-
trivial types were previously passed by const&. So if we wanted to avoid
expensive copies, we would have to const_cast and move the data.

We now pass ownership of all transferred data to the client subclasses.
This allows us to remove const_cast from these methods, and allows us to
avoid some trivial expensive copies that we didn't bother to const_cast.

Services/WebDriver/WebContentConnection.h

@@ -27,7 +27,7 @@ public:
 private:
     virtual void die() override;
 
-    virtual void driver_execution_complete(Web::WebDriver::Response const&) override;
+    virtual void driver_execution_complete(Web::WebDriver::Response) override;
 };
 
 }