Add a entity reference prop data shape preview to code editor

Lauri Timmaneerequested to merge
issue/canvas-3591805:3591805-code-editor-developers-cannot-see-what-a-content-entity-reference-prop-delivers-to-their-component into 1.x

AI was used to accelerate with the development of this MR.

Testing instructions

  • Create a new Code Component
  • Add Entity Reference Prop to the component
  • Select Content Type + Fields
  • Confirm there is an approximation of the shape that's loaded after selecting fields
  • Select a preview entity
  • Confirm there is an actual API response displayed using the preview entity

Closes #3591805

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