Update: link the small graphic to the large graphic (fixes #132)

[taylortom]

Fixes #132

Update

• Annotate _graphic.small with _adapt.linkedTo: "large", so an authoring tool can keep the small image following the large one by default instead of asking the author to select the same asset twice.

Editor annotation only — no runtime behaviour changes, existing content is untouched, and tools that don't recognise the annotation ignore it. Unlinking the pair to set breakpoint-specific artwork (or to clear small deliberately, per #116) remains available.

Testing

1. Confirm schema/component.schema.json still parses and the component renders as before — the added keyword is inert at runtime.

[taylortom]

Companion PR for the same annotation in core: adaptlearning/adapt-contrib-core#876 (issue adaptlearning/adapt-contrib-core#875).

That one adds _adapt.linkedTo: "title" to displayTitle, where the same relationship already exists but is only implied by the DisplayTitle editor name. Between the two, linkedTo describes an existing behaviour in core and a new one here, rather than being introduced for a single field — worth reviewing them together if the key itself is the question.