Update System.CommandLine to 2.0.0-beta6.25358.103 (#1240)

* Initial plan

* Update System.CommandLine version and start API migration

Co-authored-by: AArnott <[email protected]>

* Complete System.CommandLine 2.0.0-beta6.25358.103 migration

Co-authored-by: AArnott <[email protected]>

* Fixups

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: AArnott <[email protected]>
Co-authored-by: Andrew Arnott <[email protected]>

Author: Copilot

Directory.Packages.props

@@ -29,7 +29,7 @@
     <PackageVersion Include="Newtonsoft.Json.Schema" Version="4.0.1" />
     <PackageVersion Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageVersion Include="NuGet.PackageManagement" Version="6.14.0" />
-    <PackageVersion Include="System.CommandLine" Version="2.0.0-beta4.22272.1" />
+    <PackageVersion Include="System.CommandLine" Version="2.0.0-beta6.25358.103" />
     <PackageVersion Include="System.Diagnostics.Tools" Version="4.3.0" />
     <PackageVersion Include="System.Drawing.Common" Version="9.0.8" />
     <PackageVersion Include="System.Memory" Version="4.6.3" />