Problem:    About time to release Vim 9.0.
Solution:   Update the version number everywhere.

Problem:    New digraph functions use old naming scheme.
Solution:   Use the digraph_ prefix. (Hirohito Higashi, closes #8580)

Problem:    Cannot add a digraph with a leading space.  It is not easy to list
            existing digraphs.
Solution:   Add setdigraph(), setdigraphlist(), getdigraph() and
            getdigraphlist(). (closes #8580)

Problem:    No digraph for 0x2022 BULLET.
Solution:   Use "oo". (Hans Ginzel, closes #6904)