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

The Python docs for __import__ recommend using importlib.get_module().

https://docs.python.org/3/library/functions.html#__import__

> Note: This is an advanced function that is not needed in everyday
> Python programming, unlike importlib.import_module().

As importlib.get_module() uses the Python module cache and returns the
module, this also allows simplifying many module cache checks of use of
sys.modules.

importlib.get_module() has been available since Python 3.3.