Adding pcre2el

So this contrib layer sets up pcre2el or rxt (RegeXp Translator or RegeXp Tools) which is a utility for working with regular expressions in Emacs, to parse, convert, and font-lock PCRE, Emacs and rx regexps.
maybe `:defer t` may be sufficient instead of listing all the command explicitly in a `:commands` property.

Search the source of `pcre2el` for `;;;###autoload` cookies, if one of the functions you listed above has this cookie then you can remove it from the list.

If the list becomes empty then you have to explicitly tell `use-package` to defer the loading of this package with `:defer t`