Adding volta brackets to additional staves

The Volta_engraver by default resides in the Score context, and brackets for the repeat are thus normally only printed over the topmost staff. This can be adjusted by adding the Volta_engraver to the Staff context where the brackets should appear; see also the “Volta multi staff” snippet.

\version "2.24"

<<
  \new Staff { \repeat volta 2 { c'1 } \alternative { c' } }
  \new Staff { \repeat volta 2 { c'1 } \alternative { c' } }
  \new Staff \with { \consists "Volta_engraver" } { c'2 g' e' a' }
  \new Staff { \repeat volta 2 { c'1 } \alternative { c' } }
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