Add emmet support to html editor in web ui

[pgaskin]

See https://github.com/emmetio/codemirror

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.

[lunny]

Now will be https://github.com/emmetio/codemirror-plugin

[6543]

I think this is closed with #11366

feel free to ask for reopen if this is not the case