fix: Adjust Solution.cs for all platforms

[Jklawreszuk]

PR Details

As title suggests my PR allow to load sln files by adjusting slashes. Main motivation relates to future xplat GameStudio project

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have built and run the editor to try this change out.

[Jklawreszuk]

I tested this change by runing Stride.FixProjectReferences project. Seems to work now 😀

[Eideren]

Thanks !