Gui: Add default JPEG save quality (#7737)

* Update SoFCOffscreenRenderer.cpp

Set jpg screenshot capture to 100% quality vs qimage defaulting to -1

* Add default quality to JPG export

Fixed original version and use quality 90% as compromise between file size and fidelity.

src/Gui/SoFCOffscreenRenderer.cpp

@@ -121,7 +121,7 @@ void SoFCOffscreenRenderer::writeToImageFile(const char* filename, const char* c
         QByteArray ba;
         QBuffer buffer(&ba);
         buffer.open(QIODevice::WriteOnly);
-        image.save(&buffer, "JPG");
+        image.save(&buffer, "JPG", 90);
         writeJPEGComment(com, ba);
 
         QFile file(QString::fromUtf8(filename));