Add support for Ctrl+Shift+Z for "REDO"

[chinchang]

What about Ctrl+Shift+Z for "REDO"? I know that also Ctrl+Y should work in the same way, but before the editor update also Ctrl+Shift+Z was working. It would be nice to have it back for several reason :) @chinchang

Originally posted by @Gabb192 in https://github.com/cssbattle/forum/discussions/295#discussioncomment-3519111