Fix remote decoration drawing on OpenGL

On Qt 6.8 enabling the "decorate target" button doesn't do anything.
If we have to inject custom GL commands, we have to inform QtQuick
that we're doing so, so wrap our after-rendering screengrab and overlay
drawing in the appropriate calls.
Also, apparently can only be done while a pass is being recorded, so
switch the connect() from afterRendering (pass has been recorded and
finished, but not submitted) to afterRenderPassRecording (QQ2 has
drawn itself but the pass is still active).

Author: dangelog

plugins/quickinspector/quickscreengrabber.cpp

@@ -567,8 +567,18 @@ OpenGLScreenGrabber::OpenGLScreenGrabber(QQuickWindow *window)
     // Force DirectConnection else Auto lead to Queued which is not good.
     connect(m_window.data(), &QQuickWindow::afterSynchronizing,
             this, &OpenGLScreenGrabber::windowAfterSynchronizing, Qt::DirectConnection);
-    connect(m_window.data(), &QQuickWindow::afterRendering,
-            this, &OpenGLScreenGrabber::windowAfterRendering, Qt::DirectConnection);
+
+    connect(
+        m_window.data(),
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+        &QQuickWindow::afterRenderPassRecording,
+#else
+        &QQuickWindow::afterRendering,
+#endif
+        this,
+        &OpenGLScreenGrabber::windowAfterRendering,
+        Qt::DirectConnection
+    );
 }
 
 OpenGLScreenGrabber::~OpenGLScreenGrabber() = default;
@@ -609,6 +619,10 @@ void OpenGLScreenGrabber::windowAfterRendering()
     // And the gui thread is NOT locked
     Q_ASSERT(QOpenGLContext::currentContext() == m_window->rendererInterface()->getResource(m_window, QSGRendererInterface::OpenGLContextResource));
 
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+    m_window->beginExternalCommands();
+#endif
+
     if (m_isGrabbing) {
         const auto window = QRectF(QPoint(0, 0), m_renderInfo.windowSize);
         const auto intersect = m_userViewport.isValid() ? window.intersected(m_userViewport) : window;
@@ -695,6 +709,10 @@ void OpenGLScreenGrabber::windowAfterRendering()
     } else {
         emit sceneChanged();
     }
+
+#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
+    m_window->endExternalCommands();
+#endif
 }
 
 void OpenGLScreenGrabber::drawDecorations()