VO does not support aria-description

[stevefaulkner]

As reported by Adrian. Need to find an alternative

[aardrian]

Just for ref:

• macOS: Bug 260835 - AX: aria-description not exposed directly to VO users by Dian Ko
• iOS: Bug 259156 - AX: aria-description not exposed as expected by Scott O'hara

Tied up in meetings, but I'll look at the code later to see if there is a simple way to add a visually-hidden node with a guaranteed unique ID to use as an aria-describedby ref.