Fix XmlDeserializer to correctly handle nested elements and ambiguous root element selection #2337
Description
Description
- XML deserialization was incorrectly flattening nested lists by using Descendants() instead of Elements(), causing deeply nested items to be included in parent lists
- Root element selection failed when multiple elements shared the same name at different nesting levels, throwing InvalidOperationException
- RemoveNamespace method was creating null attribute entries, causing potential deserialization errors
- Generic type names containing backticks were being used as invalid XML element names
Deliverables
- Root Selection: Implement shallowest-first matching strategy that prefers direct children via Element() before searching descendants, with ordering by ancestor count
- List Deserialization: Refactor HandleListDerivative to identify container elements first, then use Elements() for direct children only instead of Descendants()
- Null Filtering: Add Where() clause in RemoveNamespace to filter out null attribute values
- Name Validation: Introduce IsValidXmlElementName() check to skip invalid XML names containing backticks from generic types
- Test Coverage: Add comprehensive unit tests covering nested lists, duplicate element names, container-based lists, and multi-level nesting scenarios