[Proposal] Deprecate or clarify usage of <legend class="is-required"> for fieldset in forms

[ruizi6]

Description: While reviewing the Forms / Fieldset required example on the Vanilla Framework website, I noticed the use of

for indicating required fields in a radio group. However, I haven't found this pattern in our Figma library, and I haven’t seen it and used in practice, either internally at Canonical or externally.

Questions:

• Is this component actively maintained and intended for use?
• If not, should we consider deprecating it from both documentation and code to reduce confusion?

References: Example on the Vanilla site

Suggestion: I propose we review this and decide whether to:

1. Deprecate it officially
2. Update its design and add it to Figma if it's still considered useful