Automatic fretboards barré

When automatic fretboards are used, barre indicators will be drawn whenever one finger is responsible for multiple strings.

If no finger indications are given in the chord from which the automatic fretboard is created, no barre indicators will be included, because there is no way to identify where barres should be placed.

\version "2.24"

\new FretBoards {
  <f,-1 c-3 f-4 a-2 c'-1 f'-1>1
  <f, c f a c' f'>1
}