Fix tag width calculation for multi-column chars

* lisp/org.el (org-align-tags-here): Fix tag width calculation for
  multi-column chars.

Some characters have multiple column width.  Calculating string width
with points gives a wrong value than actual display width.  Use
`string-width' instead.

Here is an ECM for this problem.  `M-x org-update-statistics-cookies` or
`C-c #` on bar moves the tag on the headline.

* foo [0/0]								:abc:
** child
* bar [0/0]							     :日本語:
** child
12345678901234567890123456789012345678901234567890123456789012345678901234567890
         1         2         3         4         5         6         7         8

lisp/org.el

@@ -14923,7 +14923,7 @@ If ONOFF is `on' or `off', don't toggle but set to this state."
     (if	(and (looking-at (org-re ".*?\\([ \t]+\\)\\(:[[:alnum:]_@#%:]+:\\)[ \t]*$"))
 	     (< pos (match-beginning 2)))
 	(progn
-	  (setq tags-l (- (match-end 2) (match-beginning 2)))
+	  (setq tags-l (string-width (match-string 2)))
 	  (goto-char (match-beginning 1))
 	  (insert " ")
 	  (delete-region (point) (1+ (match-beginning 2)))