tikz should reset \tikz@expandcount more frequent

[muzimuzhi]

Brief outline of the bug

As discussed in #967 (comment), currently tikz never resets \tikz@expandcount when a token handled in \tikz@handle is encountered on a path. This will raise error Giving up on this path. Did you forget a semicolon? when too many steps of expansions are executed when scanning a path.

Minimal working example (MWE)

\documentclass{article}
\usepackage{tikz}

\makeatletter
% Token "r" is handled in \tikz@handle. 
% To show the problem, redefine its handler.
\let\tikz@rect\tikz@scan@next@command

\def\oneHundredExpansions{}
\def\oneExpansion{r}

\foreach \i in {1,...,101} { % 100 passes, 101 throws error
  \g@addto@macro\oneHundredExpansions{\oneExpansion}
}
\makeatother

\begin{document}
\begin{tikzpicture}
  % One handled "r" is encountered every two expansions, but the 
  % \tikz@expandcount is never reset until the 101st expansion throws an error.
  \draw (0,0) -- (1,1) \oneHundredExpansions;
\end{tikzpicture}
\end{document}

! Package tikz Error: Giving up on this path. Did you forget a semicolon?.

@Rmano
Note that in pgf 3.1.8 and 3.1.8a, tokens handled by \tikz@handler@more will not reset the count as well. In the above example, they are ( in (0, 0), - in --, and ( in (1, 1), hence \foreach \i in {1,...,98} is enough to trigger the error. See a therefore broken circuitikz example in #967 (comment).