Allow user control on char-width of "ambiguous" characters

Allow user control on char-width of "ambiguous" characters

* src/character.c (syms_of_character) <ambiguous-width-chars>: New
char-table.

* lisp/international/characters.el (ambiguous-width-chars): Fill
the table.
(update-cjk-ambiguous-char-widths): New function.
(cjk-ambiguous-chars-are-wide): New defcustom, uses
'update-cjk-ambiguous-char-widths' as its :set function.
(use-cjk-char-width-table): Obey 'cjk-ambiguous-chars-are-wide' by
adding another child char-table for ambiguous-width characters,
where the width is set according to the option.

* lisp/language/chinese.el ("Chinese-GB", "Chinese-BIG5")
("Chinese-CNS", "Chinese-EUC-TW", "Chinese-GBK"):
* lisp/language/japanese.el ("Japanese"):
* lisp/language/korean.el ("Korean"): Add new language-info slot
'cjk-locale-symbol'.

Bug#64420