Enabled doc comments in azure_core and azure_identity packages

[LarryOsterman]

Also:

Removed a significant number of unused HTTP headers from azure_core.

[Copilot]

Pull Request Overview

This PR enables documentation warnings in the azure_core and azure_identity packages and removes a significant number of unused HTTP headers from azure_core. The changes aim to improve code documentation consistency and eliminate dead code.

Key changes include:

• Added #![warn(missing_docs)] directive to enforce documentation standards
• Added comprehensive documentation to numerous public types, methods and fields
• Simplified HTTP header constants by removing unused ones
• Made struct fields public and removed accessor methods in favor of direct field access
• Added documentation comments to macro-generated content

Reviewed Changes

Copilot reviewed 57 out of 57 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sdk/typespec/typespec_client_core/src/http/request/options/mod.rs	Added documentation to APPLICATION_JSON variant in ContentType macro
sdk/typespec/typespec_client_core/src/http/request/options/macros.rs	Enhanced macro to support documentation attributes for variants
sdk/identity/azure_identity/src/lib.rs	Added missing_docs warning directive
sdk/identity/azure_identity/src/managed_identity_credential.rs	Added comprehensive documentation to public types and methods
sdk/identity/azure_identity/src/developer_tools_credential.rs	Added method documentation and changed test helper visibility
sdk/identity/azure_identity/src/client_secret_credential.rs	Added detailed documentation for credential creation
sdk/identity/azure_identity/src/azure_pipelines_credential.rs	Added struct documentation
Multiple AMQP and messaging files	Changed from accessor methods to direct field access for better ergonomics
sdk/core/azure_core/src/lib.rs	Added missing_docs warning and documentation
sdk/core/azure_core/src/http/request/options/mod.rs	Significantly simplified by removing unused HTTP header constants
sdk/core/azure_core_*/src/lib.rs	Added missing_docs warnings and comprehensive documentation

[heaths]

There were a few other instances of warn that should be expect so we remember to clean it up in the future and not allow subsequent violations.

Mainly holding because this changes azure_core and we need to wait until after the service crates ship next week.

Also, be sure to update the sdk/core/azure_core/CHANGELOG.md file. With as many headers as you removed, you may not have to be quite so specific since we haven't even GA'd yet. Maybe even just "Remove a lot of unused headers." in Breaking Changes would be fine.

[LarryOsterman]

Marked as Draft until Core versions are updated.