GetTargetFrameworkMoniker: add support for netX.Y for TFMs ".NETCoreApp, Version=5.0" or newer.

Author: siegfriedpammer

ICSharpCode.Decompiler/CSharp/ProjectDecompiler/TargetFramework.cs

@@ -89,6 +89,8 @@ static string GetTargetFrameworkMoniker(string frameworkIdentifier, int version)
 					return "net" + GetVersionString(version, withDots: false);
 
 				case ".NETCoreApp":
+					if (version >= 500)
+						return "net" + GetVersionString(version, withDots: true);
 					return "netcoreapp" + GetVersionString(version, withDots: true);
 
 				case ".NETStandard":