Add .NET 11 breaking change doc: obsolete ModelMetadataIdentity.ForProperty overload removed

[Copilot]

ModelMetadataIdentity.ForProperty(Type modelType, string name, Type containerType), obsolete since ASP.NET Core 3.1 (dotnet/aspnetcore#15134), was removed in dotnet/aspnetcore#67077 for .NET 11 Preview 7. This adds the corresponding breaking change article.

Changes

• New article — aspnetcore/breaking-changes/11/modelmetadataidentity-forproperty-removed.md, following the standard breaking-change structure (version introduced, previous/new behavior, type of change, reason, recommended action, affected APIs). Classified as binary/source incompatible.
• aspnetcore/toc.yml — TOC entry under ASP.NET Core 11 breaking changes, in alphabetical position.
• aspnetcore/breaking-changes/11/overview.md — index table row.

Recommended migration documented in the article:

// Removed
var identity = ModelMetadataIdentity.ForProperty(
    typeof(string), "Name", typeof(Person));

// Use the PropertyInfo overload
var propertyInfo = typeof(Person).GetProperty("Name");
var identity = ModelMetadataIdentity.ForProperty(
    propertyInfo, typeof(string), typeof(Person));