(Q_canonical): New variable.

(Q_canonical): New variable.
(put_char_composition): Return a feature name: return `->canonical' if
argument `value' specifies single character.
(Fput_char_attribute): Use `put_char_composition' to determine feature
name for `=decomposition' or `->denotational'.
(Fsave_char_attribute_table): Use `Fchar_refs_simplify_char_specs' for
`->canonical'.
(syms_of_chartab): Add new symbol `->canonical'.