Add a `blocklyNotEditable` CSS class to the block's root SVG

[BeksOmega]

To Fix

In the BlockSvg class' setEditable method, call dom.addClass on the this.svgGroup_ to add a blocklyNotEditable class when the block is not editable, or dom.removeClass to remove the class when the block is editable.

The PR to fix this should be made against the rc/v12.0.0 branch.

To work on this issue, please comment below asking to be assigned.

[dianaPrahoveanu-SL]

Hi @BeksOmega can I please be assigned to this issue?

[BeksOmega]

Go for it @dianaprahoveanu23 =) Let me know if you have any questions!

[BeksOmega]

Closed by #8391