Allow opt-out of V16 style mutation convention formatting

[michaelstaib]

No description provided.

[Copilot]

Pull request overview

This PR introduces an opt-out mechanism for the newer (V16-style) mutation convention name formatting by adding a “V15-style” formatting path that preserves underscores when generating convention-derived mutation type names.

Changes:

• Renames the mutation reformatting flag on ObjectFieldConfiguration and updates the corresponding CoreFieldFlags value.
• Updates mutation convention type-name formatting to use a V15-style formatter when the new flag is enabled.
• Updates the relevant mutation convention test and helper mutation type to validate underscore-preserving behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/HotChocolate/Core/test/Types.Mutations.Tests/AnnotationBasedMutations.cs	Updates test expectations and test helper mutation type to validate V15 underscore-preserving formatting.
src/HotChocolate/Core/src/Types/Types/Descriptors/Configurations/ObjectFieldConfiguration.cs	Renames the public configuration flag and updates its documentation.
src/HotChocolate/Core/src/Types/Types/Descriptors/Configurations/CoreFieldFlags.cs	Renames the internal flag enum value backing the configuration property.
src/HotChocolate/Core/src/Types.Mutations/MutationConventionTypeInterceptor.cs	Adds V15-style formatting function and switches formatting based on the new flag.

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