• Replace calls to Marshal.PtrToStringUni and Marshal.StringToCoTaskMemUni with calls of equivalent methods on Utf16StringMarshaller throughout the repository.
• Improve type consistency by updating method signatures and fields to use ushort* instead of IntPtr for UTF-16 string pointers, removing unnecessary (IntPtr) casts.
• Add unsafe modifiers to fix unsafe context issues when using unmanaged pointers as appropriate.
• Do not change interop tests.
• Preserve original Utf16StringMarshaller.cs

cc: @copilot, @jkotas