Restore schema-evolution declarations to elasticgraph-schema_definition

[jwils]

Why

elasticgraph-proto_ingestion (#1080) is a second consumer of the schema-evolution declarations: it needs field.renamed_from metadata to keep protobuf field numbers stable across public field renames, and type.deleted_field maps directly onto protobuf reserved field numbers as a natural follow-up. With the markers living inside elasticgraph-json_ingestion (where #1259 moved them), any other consumer has to duck-type against state that may or may not be present (state.respond_to?(:renamed_fields_by_type_name_and_old_field_name)), and proto-only projects can't declare renames at all.

These declarations record serializer-neutral facts about how a schema has evolved, so this PR restores them to core elasticgraph-schema_definition (where they lived prior to #1259), partially reverting #1259's placement — the situation has changed now that two serializers consume them.

This also addresses the concern raised in review of #1259 about elasticgraph-json_ingestion bolting 9 fields onto ::ElasticGraph::SchemaDefinition::State with State & StateExtension casts: its StateExtension now adds only the 5 genuinely JSON-specific fields, and the four deprecation registries are ordinary typed State members that need no casts.

What

• Move DeprecatedElement to ElasticGraph::SchemaDefinition::SchemaElements::DeprecatedElement.
• Add the four registries (renamed_types_by_old_name, deleted_types_by_old_name, renamed_fields_by_type_name_and_old_field_name, deleted_fields_by_type_name_and_old_field_name) and their register_* methods to core State, always initialized.
• Move the DSL — field.renamed_from, type.renamed_from, type.deleted_field, schema.deleted_type — onto core Field/TypeWithSubfields/API, with docs reworded to be serializer-neutral.
• elasticgraph-json_ingestion keeps everything actually JSON-specific (schema version enforcement, merge reporting and "no longer needed" warnings, pruning), reading the core registries.
• Relocate the DeprecatedElement spec to elasticgraph-schema_definition, where it now also proves the DSL works with no extension active and that defined_at reports the user's schema definition location through the DelegateClass indirection.

No user-facing behavior changes: f.renamed_from etc. work exactly as before for json_ingestion users; they now also work without json_ingestion.

Stacked PRs

#1080 rebases on this to drop its respond_to? probe and spec shim.

Verification

• script/quick_build (all green, including script/run_gem_specs for both changed gems at 100% line + branch coverage)
• script/type_check, script/lint, script/spellcheck

References

• Move deprecated schema markers to JSON ingestion #1259 (moved the markers to json_ingestion; this partially reverts that placement)
• Add elasticgraph-proto_ingestion schema artifacts #1080 (the proto_ingestion consumer)
• Feature Proposal: Support for Protobuf ingestion #1059