Forms: verify nested Group rendering in generated forms

## Observed report

A generated Form block with the hierarchy Form > Group > Group > required text field + Button was reported to render the field and button as direct form children.

## Upstream runtime result

A WordPress block-render reproduction using the same dynamic parent callback pattern retains both static core/group wrappers and their classes around a dynamic child. The Forms runtime then passes the assembled HTML through `Contact_Form::parse()`, whose shortcode parsing preserves surrounding HTML while registering fields.

## Follow-up

Reproduce this against an environment running the Jetpack Forms package and attach the serialized block content and rendered DOM if it differs. The local sites used for the investigation do not have Jetpack installed, so no package-specific frontend regression is claimed.