ClangFormat: Move tests into plugin

That's where they belong

Change-Id: I78e33e76a2f42f05961f6fab31da5f3dd583a2e9
Reviewed-by: Artem Sokolovskii <artem.sokolovskii@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/clangformat/clangformatplugin.h

@@ -35,6 +35,7 @@ class ClangFormatPlugin : public ExtensionSystem::IPlugin
     Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QtCreatorPlugin" FILE "ClangFormat.json")
 
     bool initialize(const QStringList &arguments, QString *errorString) final;
+    QVector<QObject *> createTestObjects() const override;
 };
 
 } // namespace ClangTools