(char-db-coded-charset-priority-list): Add `=>iwds-1'.

(char-db-coded-charset-priority-list): Add `=>iwds-1'.
(char-db-decode-isolated-char): If (decode-char ccs code-point)
returns nil, define it to avoid error as a workaround.
(char-db-insert-ccs-feature): Support `=>iwds-1'.
(insert-char-attributes): Format `<-denotational@component' like
`<-denotational'.