Move richtext editor toolbar to the bottom for tasks

What does this MR do and why?

For #382589 (closed)

In tasks description, move toolbar of the richtext editor to under the editor

Doesn't change markdown plaintext editor, or move the Markdown/Richtext switcher to toolbar. Reasons in #382589 (comment 1180631126)

Rename top-toolbar to formatting-toolbar so it's not strange that it is at the bottom.

1. Enable work_items_mvc feature flag
2. Create a task on an Issue
3. Edit description
4. Check bar below editor in Rich text mode