LibGUI: Handle fast_greet stuff in WindowServerConnection constructor

Move the from handshake() to the constructor (and move the constructor
out-of-line while we're at it.)

This prepares getting rid of the handshake() mechanism since this is
the only remaining user.

Userland/Libraries/LibGUI/WindowServerConnection.cpp

@@ -41,7 +41,8 @@ static void set_system_theme_from_anonymous_buffer(Core::AnonymousBuffer buffer)
     Application::the()->set_system_palette(buffer);
 }
 
-void WindowServerConnection::handshake()
+WindowServerConnection::WindowServerConnection()
+    : IPC::ServerConnection<WindowClientEndpoint, WindowServerEndpoint>(*this, "/tmp/portal/window")
 {
     // NOTE: WindowServer automatically sends a "fast_greet" message to us when we connect.
     //       All we have to do is wait for it to arrive. This avoids a round-trip during application startup.

Userland/Libraries/LibGUI/WindowServerConnection.h

@@ -17,16 +17,12 @@ class WindowServerConnection
     , public WindowClientEndpoint {
     C_OBJECT(WindowServerConnection)
 public:
-    WindowServerConnection()
-        : IPC::ServerConnection<WindowClientEndpoint, WindowServerEndpoint>(*this, "/tmp/portal/window")
-    {
-        handshake();
-    }
-
-    virtual void handshake() override;
+    virtual void handshake() override { }
     static WindowServerConnection& the();
 
 private:
+    WindowServerConnection();
+
     virtual void fast_greet(Gfx::IntRect const&, Core::AnonymousBuffer const&, String const&, String const&) override;
     virtual void paint(i32, Gfx::IntSize const&, Vector<Gfx::IntRect> const&) override;
     virtual void mouse_move(i32, Gfx::IntPoint const&, u32, u32, u32, i32, bool, Vector<String> const&) override;