Allow separate styling for different parts of text lines

Follow up from https://github.com/musescore/MuseScore/pull/30151

Text lines have generally have three different text fields for:

• Beginning text
• Text when continuing onto a new system
• Ends text

As of this PR, it's possible to style this text in properties, but all three pieces of text get styled the same way (except for 3.X scores opened in MS4).

We need to design a way to allow changing the text style for each segment separately.

Text line objects to which this would apply:

• Volta lines
  • Prima volta
  • Seconda volta (open)
  • Seconda volta
  • Terza volta
• Ottava lines
  • 8va alta
  • 8va bassa
  • 15ma alta
  • 15ma bassa
  • 22ma alta
  • 22ma bassa
• Palm mute
• Let ring
• Text line
• System text line
• Staff text line
• Barré line
• Crescendo line
• Diminuendo line
• Line
• accel.
• allarg.
• rall.
• rit…
• calando
• lentando
• morendo
• precipitando
• smorz.
• sost…
• string.
• Straight glissando
• Wavy glissando