Issue #3582939: Fix getSupportedTypes() in MapDefinitionNormalizer and...

Issue #3582939: Fix getSupportedTypes() in MapDefinitionNormalizer and ContextDefinitionNormalizer to only handle json_schema format

Both normalizers were returning [Class => FALSE] for non-json_schema formats, causing Symfony to fall back to supportsNormalization() which matched every FieldItem via ComplexDataInterface. This made doNormalize() return NULL for all field values in REST responses.

Fix: return [] for non-json_schema formats so Symfony skips these normalizers entirely. Same pattern as MR !69 (merged) which fixed LegacyTypedDataNormalizer for issue #3568588 (closed).

Closes #3582939