Support input validation for minimal APIs via generic resolver model

[captainsafia]

Implements generic DataAnnotations-based validations resolver model and consumption in minimal APIs.

Guide for reviewers:

• Code in Http.Abstractions contains the default implementation of methods that execute validation
• Code in ValidationsGenerator is the source generator that statically discoves validatable types and emits a compile-time generated IValidatableInfoResolver
• Tests in Http.Extensions/test validate end-to-end behavior in minimal APIs and include snapshots for generated code
• Tests in Http.Abstractions/test validate the runtime behavior of the validate APIs

Address #46349.

[Copilot]

PR Overview

This PR implements a generic DataAnnotations‐based validation resolver model for minimal APIs. It introduces new types and interfaces for representing validatable types and parameters, registers validation services via DI, and adds tests to confirm the resolver chain order.

Reviewed Changes

File	Description
src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.ValidationsGenerator/Extensions/ISymbolExtensions.cs	Provides an extension to extract display names from attributes.
src/Http/Http.Abstractions/src/Validation/ValidatableTypeInfo.cs	Implements core validation logic for types including recursive validation with depth tracking.
src/Http/Http.Abstractions/src/Validation/ValidatableParameterInfo.cs	Adds parameter validation logic using DataAnnotations attributes.
src/Http/Http.Extensions/gen/Microsoft.AspNetCore.Http.ValidationsGenerator/Extensions/IncrementalValuesProviderExtensions.cs	Introduces extension methods (Distinct, Concat) for incremental values.
src/Http/Http.Abstractions/src/Validation/ValidationServiceCollectionExtensions.cs	Provides DI registration extension for validation services.
src/Http/Http.Abstractions/src/Validation/ValidatableContext.cs	Manages validation error storage and tracking of nested validation depth.
src/Http/Http.Abstractions/src/Validation/IValidatableInfoResolver.cs	Defines the interface for resolving validation metadata.
src/Http/Http.Abstractions/src/Validation/ValidatableTypeAttribute.cs	Introduces an attribute to mark validatable types.
src/Http/Http.Abstractions/src/Validation/ValidatablePropertyInfo.cs	Encapsulates member validation logic.
src/Http/Http.Abstractions/test/ValidatableInfoResolverTests.cs	Adds tests to verify resolver chain behavior and proper resolution of metadata.
src/Http/Http.Abstractions/src/Validation/ValidationOptions.cs	Configures maximum depth and chains resolvers for validation.
(Other generated model files)	Define source-generated types for validation metadata.

Copilot reviewed 44 out of 44 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

src/Http/Http.Abstractions/src/Validation/ValidatablePropertyInfo.cs:121

• The use of [result!.ErrorMessage!] to create an array is not standard C# syntax. Please update this to use a proper array initializer like 'new string[] { result!.ErrorMessage! }'.

context.AddValidationError(context.Prefix, [result!.ErrorMessage!]);