Macro editor no longer recognizes parameter description line breaks

Issue Summary

The legacy macro editor accepted simple HTML in macro parameter descriptions to allow apps to provide custom formatting of the descriptions. The new side panel based macro editor seems to have dropped support for this.

Steps to Reproduce

1. Install the minimal app using descriptor URL https://dx-standard-macro-editor-app.glitch.me/connect.json.
2. Edit a page and insert the "DX Standard Macro Editor" macro.
3. Observe the description under the Foo parameter.

Expected Results

The format of the description respects the HTML provided by the app. 

Actual Results

The description seems to be converted to plain text.

Workaround

None