MAINT: char class regex simplify (#50294)
Summary:
* remove some cases of single characters in
character classes--these can incur the overhead
of a character class with none of the benefits
of a multi-character character class
* for more details, see Chapter 6 of:
Friedl, Jeffrey. Mastering Regular Expressions. 3rd ed.,
O’Reilly Media, 2009.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50294
Reviewed By: zhangguanheng66
Differential Revision: D25870912
Pulled By: malfet
fbshipit-source-id: 9be5be9ed11fd49876213f0be8121b24739f1c13
