Buggy dvisvgm export for transparency group=knockout

[tobiasBora]

Brief outline of the bug

I'd love to be able to use the awesome transparency group=knockout feature, that allows us to paint in transparent color to reveal the underlying image. For instance (taken from the doc):

\documentclass[dvisvgm]{minimal}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
  \shade [left color=red,right color=blue] (-2,-1) rectangle (2,1);
  \begin{scope}[transparency group=knockout]
    \fill[white] (-1.9,-.9) rectangle (1.9,.9);
    \node[opacity=0,font=\fontencoding{T1}\fontfamily{ptm}\fontsize{45}{45}\bfseries]{Ti\emph{k}Z};
  \end{scope}
\end{tikzpicture}
\end{document}

is supposed to write TikZ in a rainbow-like fashion. But since this is poorly supported by pdf viewers/printers, I wanted to export to svg directly. But running:

$ lualatex --output-format=dvi test
$ dvisvgm test
$ inkscape test.svg

gives me

which is not at all the expected result as we cannot read tikz in rainbow like colors, and the huge right margin is also weird.

Thanks a lot for considering this!

NB: I asked first in mgieseki/dvisvgm#272 and they told me that tikz needed to solve it on their side.

Minimal working example (MWE)

\documentclass[dvisvgm]{minimal}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
  \shade [left color=red,right color=blue] (-2,-1) rectangle (2,1);
  \begin{scope}[transparency group=knockout]
    \fill[white] (-1.9,-.9) rectangle (1.9,.9);
    \node[opacity=0,font=\fontencoding{T1}\fontfamily{ptm}\fontsize{45}{45}\bfseries]{Ti\emph{k}Z};
  \end{scope}
\end{tikzpicture}
\end{document}