Fix double title bars with grouped floating frames

A new `DialogFloatingContainer` implementation (`SingleTitleBarDialogFloatingContainer`) is provided which always leaves
itself undecorated, but which will decorate the root pane with dialog decorations when needed. The border is also always
set to a resize border rather than sometimes having it and sometimes not. A new `DockingManager`
implementation (`MapToolDockingManager`) is needed just to instantiate `SingleTitleBarDialogFloatingContainer`.

src/main/java/net/rptools/maptool/client/ui/MapToolFrame.java

@@ -17,6 +17,7 @@
 import com.google.common.eventbus.Subscribe;
 import com.jidesoft.docking.DefaultDockableHolder;
 import com.jidesoft.docking.DockableFrame;
+import com.jidesoft.docking.DockingManager;
 import java.awt.*;
 import java.awt.event.*;
 import java.awt.image.BufferedImage;
@@ -71,6 +72,7 @@
 import net.rptools.maptool.client.ui.assetpanel.AssetPanel;
 import net.rptools.maptool.client.ui.commandpanel.CommandPanel;
 import net.rptools.maptool.client.ui.connections.ClientConnectionPanel;
+import net.rptools.maptool.client.ui.docking.MapToolDockingManager;
 import net.rptools.maptool.client.ui.drawpanel.DrawPanelPopupMenu;
 import net.rptools.maptool.client.ui.drawpanel.DrawPanelTreeCellRenderer;
 import net.rptools.maptool.client.ui.drawpanel.DrawPanelTreeModel;
@@ -619,6 +621,11 @@ public DockableFrame getFrame(MTFrame frame) {
     return frameMap.get(frame);
   }
 
+  @Override
+  protected DockingManager createDockingManager(Container container) {
+    return new MapToolDockingManager(this, container);
+  }
+
   private void initializeFrames() {
     frameMap.put(
         MTFrame.CONNECTIONS,

src/main/java/net/rptools/maptool/client/ui/docking/MapToolDockingManager.java

@@ -0,0 +1,51 @@
+/*
+ * This software Copyright by the RPTools.net development team, and
+ * licensed under the Affero GPL Version 3 or, at your option, any later
+ * version.
+ *
+ * MapTool Source Code is distributed in the hope that it will be
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License * along with this source Code.  If not, please visit
+ * <http://www.gnu.org/licenses/> and specifically the Affero license
+ * text at <http://www.gnu.org/licenses/agpl.html>.
+ */
+package net.rptools.maptool.client.ui.docking;
+
+import com.jidesoft.docking.DefaultDockingManager;
+import com.jidesoft.docking.DialogFloatingContainer;
+import java.awt.Container;
+import java.awt.Dialog;
+import java.awt.Frame;
+import java.awt.Window;
+import javax.swing.RootPaneContainer;
+
+/**
+ * Custom docking manager that creates custom floating containers.
+ *
+ * <p>This is how to use {@link SingleTitleBarDialogFloatingContainer} instead of the default
+ * implementation.
+ */
+public class MapToolDockingManager extends DefaultDockingManager {
+  public MapToolDockingManager(RootPaneContainer rootPaneContainer, Container container) {
+    super(rootPaneContainer, container);
+  }
+
+  @Override
+  protected DialogFloatingContainer createDialogFloatingContainer(
+      InternalEventManager internalEventManager, Window window) {
+    if (window instanceof Dialog dialog) {
+      return new SingleTitleBarDialogFloatingContainer(this, internalEventManager, dialog);
+    }
+
+    if (window instanceof Frame frame) {
+      return new SingleTitleBarDialogFloatingContainer(this, internalEventManager, frame);
+    }
+
+    throw new UnsupportedOperationException(
+        "JIDE Docking Framework doesn't support floating frames if rootPaneContainer is "
+            + (window == null ? "null" : window.getClass().getName()));
+  }
+}

src/main/java/net/rptools/maptool/client/ui/docking/SingleTitleBarDialogFloatingContainer.java

@@ -0,0 +1,71 @@
+/*
+ * This software Copyright by the RPTools.net development team, and
+ * licensed under the Affero GPL Version 3 or, at your option, any later
+ * version.
+ *
+ * MapTool Source Code is distributed in the hope that it will be
+ * useful, but WITHOUT ANY WARRANTY; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public
+ * License * along with this source Code.  If not, please visit
+ * <http://www.gnu.org/licenses/> and specifically the Affero license
+ * text at <http://www.gnu.org/licenses/agpl.html>.
+ */
+package net.rptools.maptool.client.ui.docking;
+
+import com.jidesoft.docking.DialogFloatingContainer;
+import com.jidesoft.docking.DockingManager;
+import com.jidesoft.docking.DockingUtils;
+import com.jidesoft.plaf.UIDefaultsLookup;
+import java.awt.Dialog;
+import java.awt.Frame;
+import java.awt.HeadlessException;
+import javax.swing.JRootPane;
+
+/**
+ * Container implementation that only decorates the root pane and not the dialog itself.
+ *
+ * <p>The default implementation ({@link com.jidesoft.docking.DialogFloatingContainer}) always
+ * decorates both the dialog and the root pane when decorations are requested, resulting in
+ * redundant title bars for docked floating frames.
+ */
+public class SingleTitleBarDialogFloatingContainer extends DialogFloatingContainer {
+  public SingleTitleBarDialogFloatingContainer(
+      DockingManager dockingManager, FloatingContainerManager floatingContainerManager, Frame frame)
+      throws HeadlessException {
+    super(dockingManager, floatingContainerManager, frame);
+  }
+
+  public SingleTitleBarDialogFloatingContainer(
+      DockingManager dockingManager,
+      FloatingContainerManager floatingContainerManager,
+      Dialog dialog)
+      throws HeadlessException {
+    super(dockingManager, floatingContainerManager, dialog);
+  }
+
+  @Override
+  public void updateUndecorated() {
+    this.setVisible(false); // So we can change the decorations.
+
+    this.setUndecorated(true);
+
+    final var dockingManager = this.getDockingManager();
+    final var contentPane = this.getContentPane();
+    if (DockingUtils.shouldUseDecoratedFloatingContainer(dockingManager, contentPane)) {
+      this.getRootPane().setWindowDecorationStyle(JRootPane.PLAIN_DIALOG);
+    } else {
+      this.getRootPane().setWindowDecorationStyle(JRootPane.NONE);
+    }
+    this.setBorder(UIDefaultsLookup.getBorder("Resizable.resizeBorder"));
+
+    this.updateBorders();
+
+    if (!this.getDockingManager().getMainContainer().isShowing()) {
+      return;
+    }
+
+    this.setVisible(true);
+  }
+}