(BUCS+518C): Separate IWDS1-0176.

(BUCS+518C): Separate IWDS1-0176.
(IWDS1-0176): New abstract node; use `<-denotational' for IWDS1-0176;
unify A-IWDSU+518A.
(U+518A): Use IWDS1-0176 instead of BUCS+518C as its mother; add
`sound@ja/on/{kan|go}' and `sound@ja/on/conventional'; add some
relations for other characters.
(U+518C): Use IWDS1-0176 instead of BUCS+518C as its mother.
(U-00020541): Likewise; add representative nodes.
(U-0002054B): Add `sound@ja/on/{kan|go}'.
(CU+2054B): Unify S-0510; add some relations for other characters.
(U-00020553): Add `<-denotational' for A-IWDSU+20553; add
`ideographic-structure'; add `<-original' for IU+21249; add
representative nodes.
(A-IWDSU+20553): New abstract node.