Add a forceLoad option to property editor (#8268)

The property editor was sometimes failing to load. I think this was the
repro:
1. Open a project (property editor will load)
2. Close the project
3. Open the project again (property editor fails to load)

It seems the static var is set to null only on IJ first startup, not on
project open. There may be a better way to fix this but I'm not sure
what it is yet.

Author: helin24

flutter-idea/src/io/flutter/propertyeditor/PropertyEditorViewFactory.java

@@ -73,32 +73,35 @@ public void createToolWindowContent(@NotNull Project project, @NotNull ToolWindo
       return;
     }
 
-    checkDockedUnpinnedAndCreateContent(project, toolWindow);
+    checkDockedUnpinnedAndCreateContent(project, toolWindow, true);
 
     final PropertyEditorViewFactory self = this;
     MessageBusConnection connection = project.getMessageBus().connect();
     connection.subscribe(ToolWindowManagerListener.TOPIC, new ToolWindowManagerListener() {
       @Override
       public void toolWindowShown(@NotNull ToolWindow activatedToolWindow) {
         if (activatedToolWindow.getId().equals(getToolWindowId())) {
-          checkDockedUnpinnedAndCreateContent(project, toolWindow);
+          checkDockedUnpinnedAndCreateContent(project, toolWindow, false);
         }
       }
 
       @Override
       public void stateChanged(@NotNull ToolWindowManager toolWindowManager, @NotNull ToolWindowManagerEventType changeType) {
         if (changeType.equals(ToolWindowManagerEventType.SetToolWindowAutoHide) ||
             changeType.equals(ToolWindowManagerEventType.SetToolWindowType)) {
-          checkDockedUnpinnedAndCreateContent(project, toolWindow);
+          checkDockedUnpinnedAndCreateContent(project, toolWindow, false);
         }
       }
     });
     Disposer.register(toolWindow.getDisposable(), connection);
   }
 
-  private void checkDockedUnpinnedAndCreateContent(@NotNull Project project, ToolWindow toolWindow) {
+  private void checkDockedUnpinnedAndCreateContent(@NotNull Project project, ToolWindow toolWindow, boolean forceLoad) {
     final Boolean isDockedUnpinned = toolWindow.getType().equals(ToolWindowType.DOCKED) && toolWindow.isAutoHide();
-    if (!isDockedUnpinned.equals(previousDockedUnpinned)) {
+
+    // If this is the first time we are loading the content, force a load even if docked unpinned state matches.
+    // Docked unpinned state is only null the first time application is opened (I think).
+    if (!isDockedUnpinned.equals(previousDockedUnpinned) || forceLoad) {
       previousDockedUnpinned = isDockedUnpinned;
       super.createToolWindowContent(project, toolWindow, isDockedUnpinned
                                                          ? "This tool window is in \"Docked Unpinned\" mode, which means it will disappear "