Multiple transpositions for Horns
In historical scores, it is common for horns in F to be transposed down a 4th for treble clef and up a 5th for bass clef. Currently it is necessary to enter a custom instrument definition for the bass clef transposition. This gets tedious and creates a new mixer entry for every instrument change.
Making this a feature would also help to clean up the instruments list a bit. For example, it could allow for a single Classical Guitar instrument that transposes if the user enters a treble clef and not transpose if the user enters a treble clef 8va below.
Relates to #311174: [EPIC] UI/UX issues and suggestions