[FEATURE] - support custom inline syntax serialization when calling serializeDocumentToMarkdown

[fatherOfLegends]

Your Info
Larry McKenzie on behalf of Open Vision Engineering

User Behavior/Feature Value
Would love a way to provide my own AttributedTextMarkdownSerializer to override the behavior of the extension toMarkdown(). Our app has custom attributed text and we deserialize to markdown + some custom elements. This means we have to duplicate every text based node serializer that uses this extension function so that we can call our own extension. Ideally we could inject this behavior via serializeDocumentToMarkdown