Add common pairs to defcustom for electric-quote-chars

Add common pairs to defcustom for electric-quote-chars

* lisp/electric.el (electric--print-list-of-chars): New function to
display chars as chars instead of integers in a custom widget.
(electric-char-pair): New widget for displaying a pair of characters.
(electric-quote-chars-pairs): New widget.  Contains presets for common
combinations of left/right quotation characters
(electric-quote-chars): Update to use 'electric-quote-chars-pairs'.

* etc/NEWS: Announce the change.

(cherry picked from commit 62d6ba2ede95805ba309bdc538628eb49b331f03)