Add glyph-images of HNG-KHM.

Add glyph-images of HNG-KHM.
(U+6551): Separate UU+6551.
(UU+6551): Add `=>ucs@iwds-1'; don't subsume HNG-KHI0406-0.
(HD-TK01036590): New character; add `<-denotational' for U+6551;
subsume g2-HD-TK01036590, HNG-KHI0406-0 and HNG-KHM0357-0.
(U+656C-itaiji-001): New character to subsume HNG-KHM0353-0 and
HNG-KHI0403-0; add `<-denotational' for U+656C.
(U-00022FBE): Don't unify JU+6577, AJ1-03537, J0-495F, GT-16902 and
M-13359'; unify MJ057611 and KOSEKI-149590; add `<-formed' for U+6577;
add HNG-KHM0354-0.
(JU+6577): Separate U-00022FBE and C6-5D4B.
(IU+22FD9): Add `<-formed' for U+6578; add HNG-KHM0356-0.