bug#41841: 26.3; reftex and tikz's labels

[phs]

It seems reftex mistakes labels in tikz nodes with genuine \label 's in
LaTeX
source.

To reproduce:

1) open a buffer foo.tex in LaTeX mode

2) insert (via cut&paste) the following text

\begin{figure}
\begin{tikzpicture}
\node at (0,0) [label={node 0}] % not a LaTeX label
\end{tikzpicture}
\caption{Figure that!}
\label{myfigure} % only genuine label
\end{figure}

3) M-x reftex-toc

4) in the TOC buffer, hit key l for reftex-toc-toggle-labels

5) now the TOC buffer shows a genuine LaTeX \label and an irrelevant
tikz node "label".

--phs

"Algebraic symbols are used when you do not know what you are talking about"

In GNU Emacs 26.3 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.20
Version 10.14.3 (Build 18D109))
 of 2019-09-02 built on builder10-14.porkrind.org
Windowing system distributor 'Apple', version 10.3.1894

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS

Important settings:
  value of $LC_ALL: en_US
  value of $LANG: en_US
  locale-coding-system: utf-8-unix

Major mode: TOC

Minor modes in effect:
  cursor-intangible-mode: t
  global-magit-file-mode: t
  magit-auto-revert-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  diff-auto-refine-mode: t
  icomplete-mode: t
  global-eldoc-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t