[Fusion] Support directive-definition deprecation and location

[glen-84]

Summary

• Fusion gateway introspection now reports the DIRECTIVE_DEFINITION directive location (added to the __DirectiveLocation enum, the location constants, and the __Directive.locations resolver), so a directive that targets directive definitions (for example @requiresOptIn) is introspected correctly instead of failing the resolver.
• Adds directive-definition deprecation to the introspection surface, matching single-server HotChocolate: FusionDirectiveDefinition carries IsDeprecated/DeprecationReason (parsed from @deprecated), __Directive exposes isDeprecated/deprecationReason, and __Schema.directives honors includeDeprecated.
• Deprecation is added via a new constructor overload; the original FusionDirectiveDefinition constructor is retained and marked [Obsolete] so existing callers keep compiling.

Test plan

• Gateway introspection test: a directive whose locations include DIRECTIVE_DEFINITION is introspected with that location, and the isDeprecated/deprecationReason fields resolve for every directive.
• Full Fusion.Execution.Tests passes (2308/0).

[Copilot]

Pull request overview

Adds support in Fusion gateway introspection for directive definitions that (1) target DIRECTIVE_DEFINITION and (2) participate in deprecation metadata, bringing Fusion’s introspection surface closer to single-server HotChocolate behavior.

Changes:

• Extend introspection schema/resolvers to include DIRECTIVE_DEFINITION in __DirectiveLocation and handle it in __Directive.locations.
• Add directive-definition deprecation metadata (isDeprecated/deprecationReason) to __Directive and honor includeDeprecated on __Schema.directives.
• Extend FusionDirectiveDefinition to carry deprecation info (new ctor overload + [Obsolete] old ctor) and parse @deprecated on directive definitions during schema completion.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/HotChocolate/Fusion/test/Fusion.Execution.Tests/Execution/Introspection/DirectiveDefinitionIntrospectionTests.cs	Adds a gateway introspection test exercising DIRECTIVE_DEFINITION and new directive deprecation fields.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Introspection/__Schema.cs	Updates __Schema.directives resolvers to support includeDeprecated filtering.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Introspection/__DirectiveLocation.cs	Adds DIRECTIVE_DEFINITION enum string constant.
src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Introspection/__Directive.cs	Exposes isDeprecated/deprecationReason and adds DIRECTIVE_DEFINITION location mapping.
src/HotChocolate/Fusion/src/Fusion.Execution.Types/FusionDirectiveDefinition.cs	Adds deprecation properties and constructor overload; marks old ctor obsolete.
src/HotChocolate/Fusion/src/Fusion.Execution.Types/Completion/IntrospectionSchema.cs	Updates introspection SDL to add new fields/args and DIRECTIVE_DEFINITION.
src/HotChocolate/Fusion/src/Fusion.Execution.Types/Completion/CompositeSchemaContext.cs	Updates built-in directive definitions to use the new deprecation-aware constructor.
src/HotChocolate/Fusion/src/Fusion.Execution.Types/Completion/CompositeSchemaBuilder.cs	Parses @deprecated on directive definitions and populates FusionDirectiveDefinition deprecation metadata.

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[github-actions]

Patch coverage

77.2% of changed lines covered (61/79)

File	Covered	Changed	Patch %
…/src/Fusion.Execution.Types/FusionDirectiveDefinition.cs	12	22	54.5% 🔴
…/src/Fusion.Execution/Execution/Introspection/__Schema.cs	15	23	65.2% 🔴
…/Fusion.Execution.Types/Completion/CompositeSchemaBuilder.cs	3	3	100.0% 🟢
…/Fusion.Execution.Types/Completion/CompositeSchemaContext.cs	8	8	100.0% 🟢
…/src/Fusion.Execution.Types/Completion/IntrospectionSchema.cs	8	8	100.0% 🟢
…/src/Fusion.Execution/Execution/Introspection/__Directive.cs	14	14	100.0% 🟢
…/Execution/Introspection/__DirectiveLocation.cs	1	1	100.0% 🟢

Uncovered changed lines (JSON)

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  "files": [
    { "path": "src/HotChocolate/Fusion/src/Fusion.Execution.Types/FusionDirectiveDefinition.cs", "ranges": [[26, 35]] },
    { "path": "src/HotChocolate/Fusion/src/Fusion.Execution/Execution/Introspection/__Schema.cs", "ranges": [[117, 118], [122, 124], [145, 146], [156, 156]] }
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}

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Project coverage: 52.5% (217015/413212 lines)