#4764 Use postfix syntax for ligatures

[Simon Albrecht]

Ligatures have for a long time been the only remaining part of LilyPond input language using infix syntax instead of postfix syntax. There’s a comment in CG 14.7:

‘Ligature brackets, I’m looking at you. (non-postfix notation must die!)’

but surprisingly there is no tracker issue yet.

As an example, { \[a1 b\] } should be { a1\[ b\] }. This would also allow much more flexibility in using the facility introduced through issue 3487.

A convert-ly rule should be provided.