Fix WriteDynamicHeader parameter to be non-nullable

[oii-nasif]

Summary

• Fixed WriteDynamicHeader method signature to accept non-nullable IDynamicMetaObjectProvider parameter
• Resolves issue DynamicObject WriteDynamicHeader issue #2355 where DynamicObject parameter handling was inconsistent

Test plan

• Run existing DynamicTests to verify WriteDynamicHeader works correctly with both ExpandoObject and DynamicObject
  types
• Verify WriteDynamicIDynamicMetaObjectProviderHasDifferentPropertyOrderingTest passes

Fixes #2355