Form Block: label formatting is not applied on the frontend

#### Steps to reproduce the issue

On a site where the Contact Form feature is enabled...

1. Go to Posts > Add New
2. Add a form block.
3. Customize the label of one of the fields; change both the text and the text formatting, like so:


4. On the frontend, the text change apppears, but not the formatting change:


I think it would be fine to remove those formatting options from the text area in the editor, since we do not really want to output HTML tags inside the `label` tag on the frontend.

Start by tracing the Contact Form form block from the editor's label control to its frontend rendering. Reproduce the issue with formatted label text, then confirm the chosen resolution by checking that formatting is either rendered correctly on the frontend or no longer offered in the editor.

Written by the indexing model from the issue text.