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

[myronmarston]

Suggested change

	# migrate data ingested under the old JSON schema version.
	# ingest events that contain old field names that are no longer in the current schema.

[myronmarston]

Suggested change

	# @note When `elasticgraph-json_ingestion` is in use and this API applies, ElasticGraph will give you an error message
	# @note In situations where this API is needed, ElasticGraph will give you an error message

[myronmarston]

Suggested change

	# @note When `elasticgraph-json_ingestion` is in use and this API applies, ElasticGraph will give you an error message
	# @note In situations where this API is needed, ElasticGraph will give you an error message

[myronmarston]

Suggested change

	# @note When `elasticgraph-json_ingestion` is in use and this API applies, ElasticGraph will give you an error message
	# @note In situations where this API is needed, ElasticGraph will give you an error message

[myronmarston]

Suggested change

	# @note When `elasticgraph-json_ingestion` is in use and this API applies, ElasticGraph will give you an error message
	# @note In situations where this API is needed, ElasticGraph will give you an error message

[myronmarston]

Instead of manually instantiating DeprecatedElement can we define a new_deprecated_element factory method and use that? That's what we had before #1259 and it's a pattern we want to consistently follow so that extensions can hook in as needed.

[myronmarston]

Suggested change

	state = define_schema(schema_element_name_form: "snake_case") do |schema|
	schema.object_type "Widget" do |t|
	t.renamed_from "OldWidget"
	t.field "id", "ID!"
	end
	end.state
	expect(state.renamed_types_by_old_name.fetch("OldWidget").defined_at.path).to eq __FILE__
	renamed_from_callsite = nil
	state = define_schema(schema_element_name_form: "snake_case") do |schema|
	schema.object_type "Widget" do |t|
	renamed_from_callsite = __LINE__ + 1
	t.renamed_from "OldWidget"
	t.field "id", "ID!"
	end
	end.state
	defined_at = state.renamed_types_by_old_name.fetch("OldWidget").defined_at
	expect(defined_at.path).to eq __FILE__
	expect(defined_at.lineno).to eq renamed_from_callsite

If we're going to verify the file is correct, we should verify the line number is correct, too--there are other stack frames from the same file in the callstack (such as the schema.object_type call) which would be the wrong line to report.

Also: can you expand this test (or add additional tests) to cover all of the renamed_from/deleted_xyz APIs? They each have defined_at: ... logic which could be wrong so it'd be good to verify they are all correct.