Add glyph-images of HNG-KHM.

Add glyph-images of HNG-KHM.
(U+5C3C): Separate UU+5C3C.
(UU+5C3C): Add `=>ucs@unicode'.
(U+5C3C-itaiji-002): New character to subsume HNG-KHI0348-0 and
HNG-KHM0033-0; add `<-denotational' for U+5C3C; add `<-formed' for
U+5C3C.
(HNG-KHI0348-0): Use `<-subsumptive' for U+5C3C-itaiji-002.
(BUCS+5C6C): New abstract node.
(U+5C5E): Add `<-denotational' for BUCS+5C6C.
(A-MJ057371): New abstract character to subsume MJ057371 and
HNG-KHM0295-0; add `<-denotational' for BUCS+5C6C; add `<-formed' for
U+5C5E and U+5C6C.
(MJ057371): New character; add `<-subsumptive' for A-MJ057371; unify
KOSEKI-088400.
(U+5C6C): Add `<-denotational' for BUCS+5C6C.