FieldObjectPropsExpression::fromString() fails on expression that traverses multiple levels of entity references

Overview

I've been building some content templates, by hand, for Drupal CMS. We need to be able to return image shapes to SDC props, like {image_url, alt}, from a normal two-level media reference field on a node.

You would think a prop expression like this would do the trick (assuming that yo_ho is a normal media reference field):

'ℹ︎␜entity:node:foo␝yo_ho␞␟{src↝entity␜␜entity:media:image␝field_media_image␞␟entity␜␜entity:file␝uri␞␟url,alt↝entity␜␜entity:media:image␝field_media_image␞␟alt}'

But you'd be wrong, because there is a bug in FieldObjectPropsExpression::fromString(). The nature of the bug, according to Wim in Slack:

• \Drupal\experience_builder\PropExpressions\StructuredData\ReferenceFieldPropExpression allows chaining of references: public readonly ReferenceFieldPropExpression|FieldPropExpression|FieldObjectPropsExpression $referenced
• BUT FieldObjectPropsExpression::fromString()’s logic does not yet do that:
  

          $objectPropsToFieldTypeProps[$sdc_obj_prop_name] = new ReferenceFieldPropExpression(
            new FieldPropExpression($entity_data_definition, $field_name, NULL, $field_instance_prop_name),
            FieldPropExpression::fromString(self::PREFIX . $field_prop_ref_expr)
          );
  

Proposed resolution

It's a one-line fix. We need to call StructuredDataPropExpression::fromString(), not FieldPropExpression::fromString().