[Accessibility] Plugin dialogs are inaccessible in MS4

Issue type

UI bug

Bug description

Keyboard navigation and screen reader accessibility doesn't work in dialogs spawned by plugins.

Steps to reproduce

1. Enable any plugin with a dialog (e.g. the built-in plugin "Configure Courtesy Accidentals").
2. Open or create a score (some plugins only work when a score is open).
3. Go to Plugins > Composing/arranging tools > Configure Courtesy Accidentals.

The plugin dialog will appear but it is not navigable by keyboard or accessible to screen readers.

Screenshots/Screen recordings

MuseScore Version

4.0.2

Regression

Yes, this used to work in MuseScore 3.x and now is broken

Operating system

Windows

Additional context

At past in Musescore 3, as long as a plugin has a dialog, we blind can work in it. But in Musescore 4, it doesn't work at all. Just tried, I can enable and disable plugins in the management panel, but all plugins can't be operated using screen reader. When activating a plugin, Musescore will pop up a window where I can do nothing. Our braille music team is trying to make a plugin to send the Musescore file to braille translation module server to get a perfect braille file, but it seems we can't go any farther at this time.