Let Plugin Windows Be Maximized on X11 (#16335)

wxGTK types every wxDialog as a dialog window, and Mutter offers no
maximize for anything but a normal window, so the maximize button and
shortcut did nothing on GNOME under X11. Modeless plugin windows are now
normal windows, kept off the taskbar as before. Modal ones stay dialogs
so the window manager keeps routing focus from the main window to them.

src/slic3r/GUI/WebDialog.cpp

@@ -13,6 +13,10 @@
 #include <wx/gdicmn.h>
 #include <wx/webview.h>
 
+#ifdef __WXGTK__
+#include <gtk/gtk.h>
+#endif
+
 namespace Slic3r { namespace GUI {
 
 WebDialog::WebDialog(wxWindow*          parent,
@@ -52,6 +56,17 @@ WebDialog::WebDialog(wxWindow*          parent,
     Bind(wxEVT_CLOSE_WINDOW, &WebDialog::on_close_window, this);
 }
 
+void WebDialog::use_normal_window_type()
+{
+#ifdef __WXGTK__
+    // wxGTK types every wxDialog as a dialog, and Mutter offers no maximize for anything but a
+    // normal window. Mutter also stops hiding a normal window from the taskbar, so keep it hidden
+    // as a dialog with a parent is everywhere else.
+    gtk_window_set_type_hint(GTK_WINDOW(m_widget), GDK_WINDOW_TYPE_HINT_NORMAL);
+    gtk_window_set_skip_taskbar_hint(GTK_WINDOW(m_widget), TRUE);
+#endif
+}
+
 void WebDialog::add_user_scripts()
 {
     if (wxWebView* wv = browser()) {