fix #24001: add "Text Style..." to context menu

open text style dialog, pre-set to text style of selected element
handle chord symbols
suppress "Text Style" in menu for unstyled text

Chord symbols treated as styled for this purpose, since the chord symbol
text style is always used.
Merge pull request #700 from MarcSabatella/24001-text-style-context

fix #24001: add "Text Style" to context menu