Exclude CsWinRT-required partial types from MA0204

[Copilot]

MA0204 was flagging partial as unnecessary in multi-targeted MAUI/Windows scenarios where CsWinRT requires the type to remain partial for WinRT AOT/trimming compatibility. This produced contradictory guidance: MA0204 suggested removing partial, while the Windows build required it.

• Analyzer behavior

  • Keep partial when the type may participate in CsWinRT AOT generation.
  • Detect common WinRT-mapped interfaces (for example IDisposable, collection interfaces, INotifyPropertyChanged, ICommand) and skip MA0204 for those types.
  • Preserve partial on containing types when a nested type requires it.

• Scope of the exemption

  • Apply the exemption when CsWinRT support is present in the compilation.
  • Fall back to Windows-target detection from analyzer config build properties when CsWinRT types are not directly available.

• Coverage

  • Add focused tests for:
    • a partial class implementing IDisposable
    • the non-Windows case, which should still report MA0204
    • a containing partial type with a nested CsWinRT-relevant type

• Documentation

  • Update MA0204 docs to mention the CsWinRT/MAUI Windows exception.

Example:

public partial class CertificateHolder : IDisposable
{
    public void Dispose()
    {
    }
}

With this change, MA0204 no longer suggests removing partial from types like the above when that modifier may be required by CsWinRT on Windows-targeted builds.

• Fixes .NET MAUI project and the MA0204 "Remove unnecessary partial modifier" rule #1450