Add complex collection support to PropertyValues

[AndriySvyryd]

Part of #31237

This pull request extends PropertyValues and derived types to handle complex collection properties and adds an error message in the Cosmos provider strings. It also fixes some bugs in complex collection change detection.

Enhancements to PropertyValues:

• PropertyValues.cs: Extended the class to support complex collection properties, including methods for cloning, setting values, and converting complex collections to objects. Introduced new properties like ComplexCollectionProperties for managing complex type collections.

Validation for complex type collections:

• CosmosModelValidator.cs: Throw for complex type collections on Cosmos.

[Copilot]

Pull Request Overview

This PR enhances the PropertyValues infrastructure in EF Core to fully support complex collection properties. It adds new APIs and internal logic to:

• Store, clone, and materialize complex collections in PropertyValues, EntryPropertyValues, and ArrayPropertyValues.
• Detect, reorder, and track state changes in complex collection entries via InternalEntryBase and ChangeDetector.
• Provide empty and populated materializers for complex types in EntityMaterializerSource.
• Surface a clear error when complex type collections are used with the Cosmos provider.

Reviewed Changes

Copilot reviewed 36 out of 38 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/EFCore/ChangeTracking/PropertyValues.cs	Added IComplexProperty indexer, ComplexCollectionProperties, and abstracted SetValues to support complex collections.
src/EFCore/ChangeTracking/Internal/InternalEntryBase.cs	Extended original/current value logic to reorder and detect complex collection entries on state changes.
src/EFCore/ChangeTracking/Internal/ChangeDetector.cs	Enhanced DetectComplexCollectionChanges to handle additions, removals, moves, and null elements in complex collections.
src/EFCore/ChangeTracking/Internal/ArrayPropertyValues.cs	Added storage for nested ArrayPropertyValues lists and logic to populate complex objects in ToObject().
src/EFCore/Query/Internal/EntityMaterializerSource.cs	Initialize complex collections to null during materialization and added public methods to get materializers for complex types.
src/EFCore.Cosmos/Infrastructure/Internal/CosmosModelValidator.cs	Throw an exception for unsupported complex type collections in the Cosmos provider.

Files not reviewed (2)

• src/EFCore.Cosmos/Properties/CosmosStrings.Designer.cs: Language not supported
• src/EFCore/Properties/CoreStrings.Designer.cs: Language not supported

Comments suppressed due to low confidence (1)

src/EFCore/Query/IEntityMaterializerSource.cs:83

• [nitpick] The XML documentation for GetMaterializer and GetEmptyMaterializer still refers to "entity type" and mentions caching, but these methods now target complex types and always compile a new delegate. Update the <summary> and <param> tags to correctly describe complex type materialization and clarify that the returned delegate is not necessarily cached.

    ///     <para>

[roji]

🐑 🇮🇹 on some parts of change detection, but overall understandable and LGTM.