add first Qt6 version of musredit, mupp, etc.

src/musredit_qt6/musredit/latex_images/tfCos.tex

@@ -0,0 +1,9 @@
+\documentclass[12pt]{article}
+\pagestyle{empty}
+\begin{document}
+
+\begin{displaymath}
+\cos\left(2\pi\nu t + \phi\pi/180\right)
+\end{displaymath}
+
+\end{document}