backends/x11: Remove dependency on GLTexture::toImage

It is being phased out. Instead, read the pixels from the
cursor's framebuffer using `glReadPixels`.

Signed-off-by: Victoria Fischer <victoria.fischer@mbition.io>

src/backends/x11/windowed/x11_windowed_egl_backend.cpp

@@ -118,8 +118,13 @@ std::optional<OutputLayerBeginFrameInfo> X11WindowedEglCursorLayer::beginFrame()
 
 bool X11WindowedEglCursorLayer::endFrame(const QRegion &renderedRegion, const QRegion &damagedRegion)
 {
-    const QImage buffer = m_texture->toImage().mirrored(false, true);
-    m_output->cursor()->update(buffer, m_hotspot);
+    QImage buffer(m_framebuffer->size(), QImage::Format_RGBA8888_Premultiplied);
+
+    GLFramebuffer::pushFramebuffer(m_framebuffer.get());
+    glReadPixels(0, 0, buffer.width(), buffer.height(), GL_RGBA, GL_UNSIGNED_BYTE, buffer.bits());
+    GLFramebuffer::popFramebuffer();
+
+    m_output->cursor()->update(buffer.mirrored(false, true), m_hotspot);
 
     return true;
 }