text: Title: Newlines should not be scaped when using setting usetex=True
  Body: The documentation mentions this behavior, but only as a passing note in the middle of the tutorial.
  
  https://github.com/matplotlib/matplotlib/blob/f94fce68abe66f29e3045d0d4f20ccd0effa6767/galleries/users_explain/text/usetex.py#L87-L94
  
  When passing slightly complex latex code to matplotlib, a user might be tempted to use multi-line strings, and the error that matplotlib produces is quite cryptic. For example,
  ```python
      ax.annotate(text=r"""\begin{tabular}{cc} 
          a & b \\ 
          c & d 
      \end{tabular}""", xy=(0.5,0.5), xycoords="figure fraction", xytext=(0,0))
  ```
  produces
  ```
  RuntimeError: latex was not able to process the following string: b'\\\\begin{tabular}{cc} '
  ```
  I think it would be better to fix this behavior, but if not, it would be nice to give more visibility to it or include it in the [troubleshooting](https://github.com/matplotlib/matplotlib/blob/f94fce68abe66f29e3045d0d4f20ccd0effa6767/lib/matplotlib/text.py#L1282-L1297) at the end of the same page, at least.