HackStudio: Properly close previous project when opening a new one

Previously files in the open files view would stay open from the
previous project, and files in the new project with the same name as
files in the old one would be inaccessible, with the old ones showing
up instead. Now all files and open editors are closed before a new
project is opened.

Fixes #9103

Userland/DevTools/HackStudio/HackStudioWidget.cpp

@@ -192,6 +192,13 @@ void HackStudioWidget::open_project(const String& root_path)
         perror("chdir");
         exit(1);
     }
+    if (m_project) {
+        m_editors_splitter->remove_all_children();
+        m_all_editor_wrappers.clear();
+        m_open_files.clear();
+        m_open_files_vector.clear();
+        add_new_editor(*m_editors_splitter);
+    }
     m_project = Project::open_with_root_path(root_path);
     VERIFY(m_project);
     if (m_project_tree_view) {