Newlines should not be scaped when using setting usetex=True

Nobody has claimed this yet.

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.

Reproduce the multiline example with usetex=True, then read galleries/users_explain/text/usetex.py at the linked lines and the troubleshooting section in lib/matplotlib/text.py. Determine whether the issue is addressed by changing newline handling or by clarifying the documentation; done means the chosen behavior is documented or the example no longer produces the cryptic LaTeX error.

Written by the indexing model from the issue text.