14,0.0 Polyfill Compatibility

Light.GuardClauses 14.0.0

• Single-Source-File: use NET8_0_OR_GREATER instead of NET_8_0 to play nicely with newer .NET versions
• Breaking Change: Check.Contains(string, string, System.StringComparison) now exists in Light.GuardClauses.FrameworkExtensions to avoid conflict with other polyfill libraries

What's Changed

• fix: use NET8_0_OR_GREATER for ifdefs by @cdonnellytx in #130
• 💣 feat: play nice with PolyfillLib by @cdonnellytx in #131

Full Changelog: v13.1.0...v14.0.0