Referenced entities not resolved to current language translation in Evaluator

Overview

When Canvas evaluates prop expressions that traverse entity references (e.g., a paragraph referencing a media entity, or an entity_reference field pointing to a taxonomy term), the referenced entities are
always returned in their default language — not the current page/content language. On multilingual sites, this means component props populated from referenced entities display untranslated content.
Steps to reproduce:
1. Enable content translation on a referenced entity type (e.g., Media, Taxonomy term)
2. Create a Canvas component with a prop sourced from a reference field (e.g., image → entity reference → media → file URI)
3. Create content in the default language, translate the referenced entity
4. View the page in the translated language
5. The referenced entity's field values appear in the default language, not the translated one

Root cause:
Evaluator::doEvaluate() follows DataReferenceInterface to load referenced entities but never calls getTranslation() on them. The referenced entity is used as-is from the reference property, which returns it
in the default/stored language.

Proposed resolution

- Add a resolveTranslation() helper that checks TranslatableInterface and calls getTranslation($language_code) when a translation exists
- Thread $language_code through the entire evaluate()/doEvaluate() recursion chain
- At the entry point (EntityFieldPropSource::evaluate()), seed $language_code from the host entity's language; fall back to current language via LanguageManager
- Apply resolveTranslation() at every point a referenced entity is resolved (3 locations in doEvaluate())

User interface changes