convert-ly for note/rest-markup

[Thomas Morley]

Hi,

with e35b7959dfe the note-markup-command was changed to need a
duration-argument, before it was a string.
With, MR 627 "Revisit rest-markup-commands"
https://gitlab.com/lilypond/lilypond/-/merge_requests/627
I attempt to do similar for the rest-markup-command.

This change would need a convert-rule, imho.
Alas, this is beyond my capabilities.

Any volunteer?

Btw, e35b7959dfe contains a convert-rule for the note-markup, though
it does not seem to work.

Using convert-ly from recent master, running over a file containing:

%%%%%%%%%%%%%%
\version "2.18.2"
\markup \note #"4." #UP

%%%%%%%%%%%%%%

returns:

convert-ly atest-107.ly
convert-ly (GNU LilyPond) 2.23.1

convert-ly: Processing `atest-107.ly'...
Applying conversion: 2.19.2, 2.19.7, 2.19.11, 2.19.16, 2.19.22,
2.19.24, 2.19.28, 2.19.29, 2.19.32, 2.19.39, 2.19.40, 2.19.46,
2.19.49, 2.20.0, 2.21.0, 2.21.2


\version "2.21.2"
\markup \note #"4." #UP


cc-ing David


Thanks,
  Harm