(U+5942): Add `<-denotational@usage' for BUCS+5950; apply new

(U+5942): Add `<-denotational@usage' for BUCS+5950; apply new
conventions for glyph granularity.
(U-00021662): New character.
(U-00021674): New character.
(U-00021684): New character.
(A-cgnU+21687): New abstract node.
(U-00021687): Add `<-denotational' for A-cgnU+21687.
(A-U+21687-itaiji-001): New abstract node; use `<-denotational' for
A-cgnU+21687.
(U+21687-itaiji-001): New character; use `<-denotational' for
A-U+21687-itaiji-001.
(U-0002168B): New character.
(U-0002168E): New character.
(U-00021699): Apply new conventions for glyph granularity.
(U-00021698): New character.
(BUCS+5950): New abstract node.