plugins/screencast: Make region screen cast nicer to memfd

Set the FlipY flag so when the memfd code grabs the texture contents, it
doesn't need to flip the texture on the cpu side.

src/plugins/screencast/regionscreencastsource.cpp

@@ -59,6 +59,7 @@ void RegionScreenCastSource::updateOutput(Output *output)
 
         ShaderBinder shaderBinder(ShaderTrait::MapTexture | ShaderTrait::TransformColorspace);
         QMatrix4x4 projectionMatrix;
+        projectionMatrix.scale(1, -1);
         projectionMatrix.ortho(m_region);
         projectionMatrix.translate(outputGeometry.left(), outputGeometry.top());
 
@@ -82,6 +83,7 @@ void RegionScreenCastSource::ensureTexture()
         if (!m_renderedTexture) {
             return;
         }
+        m_renderedTexture->setContentTransform(OutputTransform::FlipY);
         m_renderedTexture->setFilter(GL_LINEAR);
         m_renderedTexture->setWrapMode(GL_CLAMP_TO_EDGE);