[Accessibility] Speech for musical symbols in text

During text and lyrics editing, screen readers read ordinary text characters but they do not read SMuFL characters (musical symbols) that are part of the text. This affects mixed dynamics (e.g. "sempre p") and any characters that the user adds from the "Musical Symbols" tab of the Insert Special Characters dialog (shortcut: F2 in MuseScore 3, Shift+F2 in MuseScore 4).

To reproduce:

1. Start a screen reader running and then launch MuseScore 3 or 4.
2. Create a new score.
3. Add a p (piano) dynamic.
4. Edit the dynamic and type "sempre" before the p so it reads "sempre p".
5. Use the left and right arrow keys to move the editing caret between the letters.
6. Press Ctrl+A (Mac: Cmd+A) to select all the letters in the dynamic.

Expected behavior:

The screen reader should say:

• "p" or "piano" when the editing caret moves next to the p character.
• "sempre p" or "document selected" when you select all characters in the dynamic.

Actual behavior:

The screen reader says:

• Nothing or "blank" when the cursor moves next to the p character.
• Just "sempre" without "p" when all characters in the dynamic are selected (Narrator says "document selected", which is ok).

Platform

• MuseScore 3: Windows running NVDA
• MuseScore 4: Windows (Narrator or NVDA), macOS (VoiceOver), Linux (Orca)