Update PostscriptQRCode so it runs on Linux

[Shane32]

Summary

• Updates PostscriptQRCode so it runs on all platforms except .NET Standard 1.3
• Adds tests for PostscriptQRCode

Notes

• Although I added tests to validate existing functionality, I did not attempt printing any of the postscript output to verify it myself.
• No functionality changes were made to PostscriptQRCode.

[codebude]

I'm confused. How does this work? The PostscriptQRCode uses System.Drawing multiple times (Color, Size, ...), but per my knoweldge System.Drawing isn't available on non-Windows platforms any longer: https://learn.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/system-drawing-common-windows-only

Thus I thought that PostscriptQRCode can't work on non-Windows platforms.
See also: #484

[Shane32]

Color and Size are located in the System.Drawing.Primitives assembly which is still supported - not System.Drawing.Common. They are basically just structs and constants.

See documentation here:

https://learn.microsoft.com/en-us/dotnet/api/system.drawing?view=net-8.0

Some types in the System.Drawing namespace rely on GDI+, which is not supported in Windows services and ASP.NET Core and ASP.NET apps. These types are in the System.Drawing.Common NuGet package and include System.Drawing.Bitmap and System.Drawing.Font. However, primitive types in the namespace, such as System.Drawing.Color, System.Drawing.Size, System.Drawing.Point, and System.Drawing.Rectangle, can be used in any application.