Block mover icons miss reqiured attributes for accessibility

[afercia]

The block mover icons were refactored in #4631 and now a svg icon is passed directly as a prop.

The problem of passing icons this way is they lack the attributes aria-hidden="true" role="img" focusable="false"

All the Dashicons use these attributes by default. Also icons passed directly should use them.

One of the consequences is that without focusable="false" the icons are focusable in Internet Explorer so there's the need to tab twice when navigating with the keyboard.

Also, icons should be hidden from assistive technologies so they also use aria-hidden="true" role="img".

I'd suggest to consider a way to check for the presence of these attributes when passing icons directly.