\let command for two csnames wrong in pgfsys-dvipdfmx.def

[u-fischer]

from https://tex.stackexchange.com/a/625313/2388

The \let command is faulty in \pgf@sys@pdf@install@mask:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{shadows.blur}

\makeatletter
\def\pgf@sys@pdf@install@mask#1{%
  \pgfutil@addpdfresource@extgs{%
    /pgfsmask\csname pgfsmaskxform@#1\endcsname\space <<
      /SMask <<
        /S /Luminosity
        /G @pgfsmask\csname pgfsmaskxform@#1\endcsname
      >> >>}%<<
  %\expandafter\let\csname pgfsmask@#1\endcsname\expandafter\csname pgfsmaskxform@#1\endcsname%<---wrong
  \expandafter\let\csname pgfsmask@#1\expandafter\endcsname\csname pgfsmaskxform@#1\endcsname%
}
\makeatother


\begin{document}
\tikz{\node[draw, fill=white, blur shadow] {A};}  % Writes 17 [in nullfont]
%
\tikz{\node[draw, fill=white, blur shadow] {B};}  % Writes 18 [in nullfont]
%
\tikz{\node[draw, fill=white, blur shadow] {C};}  % Writes 19 [in nullfont]
\end{document}