[C# Generator] Populate attributes from custom code properties and fields in NamedTypeSymbolProvider

[Copilot]

NamedTypeSymbolProvider.BuildProperties() and BuildFields() never passed symbol attributes to the PropertyProvider/FieldProvider constructors, so CustomCodeView.Properties[*].Attributes and CustomCodeView.Fields[*].Attributes were always empty. This blocked downstream consumers (e.g., mgmt generator) from detecting attributes like [Obsolete] on custom code properties and fields.

Changes

• NamedTypeSymbolProvider.cs: Extract AttributeData from each IPropertySymbol and IFieldSymbol and pass as attributes: parameter when constructing PropertyProvider and FieldProvider. All attributes (including internal CodeGen attributes) are passed through without filtering. Uses .ToArray() because the constructor's (attributes as IReadOnlyList<AttributeStatement>) ?? [] silently drops unmaterialized IEnumerable.

new PropertyProvider(
    ...,
    this,
    attributes: propertySymbol.GetAttributes().Select(a => new AttributeStatement(a)).ToArray())

new FieldProvider(
    ...,
    attributes: fieldSymbol.GetAttributes().Select(a => new AttributeStatement(a)).ToArray())

• FieldProvider.cs: Updated InitializeParameter() to filter out codegen-related attributes (from the Microsoft.TypeSpec.Generator.Customizations namespace) when propagating field attributes to constructor parameters via AsParameter. This ensures user-facing attributes like [Obsolete] propagate to generated constructor parameters, while internal codegen attributes like [CodeGenMember] do not appear in generated code. The field itself retains all attributes for downstream consumers.

var paramAttributes = Attributes.Where(a => a.Type.Namespace != CodeModelGenerator.CustomizationAttributeNamespace).ToArray();
_parameter = new(() => new ParameterProvider(
    ..., attributes: paramAttributes));

• Test: Added CanReadPropertyAttributes with a custom code file declaring [Obsolete] (with a named argument DiagnosticId), [EditorBrowsable], and a custom non-system attribute on a property, plus [Obsolete] on a field. The test validates attribute types using CSharpType.Equals, checks argument counts, validates PositionalArguments, and ensures the generator does not throw for custom non-system attributes.

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commit: ecf9570