ligature bracket engraver

[PálBenkő]

hi list,

ligature bracket engraver creates a spanner,
but there's a slight difference from other spanners:
a ligature bracket should end *after* the last note,
even if it's the first note after a line break.

I'm happy to work on this, but I need guidance.

p

------------------------------------------------------->8
{
  \[ b1
     \break
     b1 \]
}