#489 fadings with xelatex can't be used in different sizes

[U_Fischer]

xelatex (and latex/dvipdfmx) uses for fadings \pgfsys@fadingfrombox. This means that fadings can't be used in different sizes:

\documentclass{report}

\usepackage{tikz}
\usetikzlibrary{fadings}

\definecolor{lightGrey}{gray}{0.94}

\pagestyle{empty}

\begin{document}

\pgfdeclarefading{fading2}
{\tikz \shade[left color=pgftransparent!0,
right color=pgftransparent!100] (0,0) rectangle (2,2);}
\begin{tikzpicture}
\fill [black!20] (0,0) rectangle (2,2);
\pgfsetfading{fading2}{\pgftransformshift{\pgfpoint{1cm}{1cm}}}
\fill [red] (0,0) rectangle (2,2);
\end{tikzpicture}


\pgfdeclarefading{fading2}
{\tikz \shade[left color=pgftransparent!0,
 right color=pgftransparent!100] (0,0) rectangle (4,4);}
\begin{tikzpicture}
\fill [black!20] (0,0) rectangle (4,4);
\pgfsetfading{fading2}{\pgftransformshift{\pgfpoint{2cm}{2cm}}}
\fill [red] (0,0) rectangle (4,4);
\end{tikzpicture}

\end{document}

This means that e.g. drop shadows don't work at different sizes with xelatex. See e.g. https://tex.stackexchange.com/questions/445248/tikzpicture-blur-show-up-incorrectly/445321#445321