Use case

This is a follow-up of closed #97894.
iOS and macOS platforms support AccessibilityHeadingLevel which is an equivalent of ARIA: heading role on web.
iOS support was mentioned by both the OP and in the comment: #97894 (comment) but the related PR #41435 added the heading level support for the web only.

Different heading levels can speed up the navigation in case of VoiceOver users. They can quickly navigate between subsequent headings (either any or at the same level only) using the keyboard shortcuts: https://support.apple.com/guide/voiceover/search-commands-cpvokys08/mac

Proposal

Required changes are analogous to those made in flutter/engine#41435 for web.
Here is how to set the heading level: https://developer.apple.com/documentation/swiftui/view/accessibilityheading(_:)

iOS/macOS also have 6 heading levels (from 1 to 6) like web. The value of 0 can probably be mapped to unspecified.