[Build] fix: Improve StridePlatform determination accuracy

[ds5678]

PR Details

This improves the logical consistency for determining StridePlatform, StridePlatforms, and StridePlatformDeps. The files Stride.Build.props, Stride.Core.props, and Stride.Core.targets each failed to have exhaustiveness over the possible platforms.

Related Issue

This is related to #2460 and #1151.

I think this resolves #1151 because I did a text search for StridePlatform and could not find any other places that set the property, but I couldn't actually reproduce the issue being fixed. I think my lack of reproduction is due to MSBuild using old files or something.

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.