getFontsFromRichText

Every font face a rich-text document needs, in first-seen order.

Fonts have to be loaded *before* the text is painted, or the shape is measured against a fallback and then reflows when the real face arrives — which on a canvas means every shape below it moves. So the document is walked ahead of render, and this is that walk.

initialState is the base font, from the shape's own font and size props; marks on the way down override it. An app that has added its own formatting marks supplies a visitor through options.text.addFontsFromNode and wraps defaultAddFontsFromNode to keep the built-in behaviour.