Refs: #6890

The comma character is not TeX-escaped because it is frequent in general
text and escaping it would make the LaTeX output larger for only dealing
with the problem of the LaTeX-ligature of ,, into a single character.
And one there is problem with the commas in options to Verbatim from
PygmentsBridge.

The hyphen character is escaped (not in ids and URIs!) to
\sphinxhyphen{} for both Unicode and non-Unicode engines. This is needed
to work around hyperref transforming -- and --- from section titles into
EN DASH resp. EM DASH in PDF bookmarks.

https://github.com/latex3/hyperref/issues/112

Note to expert LaTeX users: if Sphinx latex user with xelatex has

- turned off Smart Quotes for some reason,

- but does want TeX ligatures and thus overrode Sphinx
latex_elements['fontenc'] default (since #6888) to this effect,

then this should be added to LaTeX preamble:

    \def\sphinxhyphen#1{-}% (\protected is now not needed)
    \let\sphinxhyphenforbookmarks\sphinxhyphen

Closes #6876

	modified:   sphinx/texinputs/sphinxmulticell.sty

In case a code-block is in an environment already using the "framed"
package, measure the vertical size needed for the code lines and use a
nested "framed" only if short enough (i.e. at most 90% of text area on a
page).

Long nested contents will drop the inner frame. They lose the background
color as well as the continuation hints across pagebreaks. But the
caption if present is typeset normally. And highlighted lines and line
numbers are rendered with no alteration.

Short nested contents (should) render exactly as before this commit:
they use "framed" but this must be encapsulated in an unbreakable
"minipage". All decoration including caption are obeyed but of course
not the continuation hints are these never apply.

Default configuration is to allow the linebreak after the backslash.
It is possible at user side via 'preamble' key and some LaTeX code
to allow the linebreak before the backslash, but each of inline-literal,
code-block, and parsed-literal has its more or less cumbersome way for
that.

Closes: #6000, #6001

This commit handles only the \ character, which had been left aside
by accident so far. Inline-literals could break at more characters
but this is not yet done in this commit. In this context, in future
it could be useful to modify sphinx.util.texescape to use mark-up
such as \sphinxtextbackslash rather than naked \textbackslash and
similarly for some other characters. This could then be used to
allow linebreaks even in regular text paragraphs.