Fix docs issues

[gewarren]

• The references to DisplayNameInfo weren't resolving in docs, presumably because they are resolving to the internal property of the same name.
• The references to DefaultValidationLocalizer fail because it's internal (and internal types aren't published on Learn).

See dotnet/dotnet-api-docs#12732.

[Copilot]

Pull request overview

This PR updates XML documentation in the Microsoft.Extensions.Validation area to avoid broken/unresolvable API doc links on Learn caused by <see cref="..."/> references pointing at internal members/types.

Changes:

• Adjusts constructor <param> docs in Validatable*Info types to avoid <see cref="DisplayNameInfo"/> resolving to the internal DisplayNameInfo property.
• Removes <see cref="DefaultValidationLocalizer"/> references from public extension method docs because the type is internal.
• Tweaks phrasing in the localization extension docs to describe the default localizer without referencing the internal implementation type.

Reviewed changes

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

File	Description
src/Validation/src/ValidatableTypeInfo.cs	Updates XML doc param text for displayNameInfo to avoid broken cref binding.
src/Validation/src/ValidatablePropertyInfo.cs	Updates XML doc param text for displayNameInfo to avoid broken cref binding.
src/Validation/src/ValidatableParameterInfo.cs	Updates XML doc param text for displayNameInfo to avoid broken cref binding.
src/Validation/Localization/src/ValidationLocalizationServiceCollectionExtensions.cs	Removes internal-type cref references and rewords docs for the default localization wiring.