Lucene.Net.Util.Constants: Added version detection for .NET Framework…

… 4.8.1. Updated FreeBSD/SunOS detection use uppercase strings as was done in the tests in dotnet/runtime (note I don't believe SunOS is currently supported, but maybe someday it will be).

src/Lucene.Net/Util/Constants.cs

@@ -64,15 +64,15 @@ public static class Constants // LUCENENET specific - made static because all me
 
         /// <summary>
         /// True iff running on SunOS. </summary>
-        public static readonly bool SUN_OS = RuntimeInformation.IsOSPlatform(OSPlatform.Create("SunOS"));
+        public static readonly bool SUN_OS = RuntimeInformation.IsOSPlatform(OSPlatform.Create("SUNOS"));
 
         /// <summary>
         /// True iff running on Mac OS X </summary>
         public static readonly bool MAC_OS_X = RuntimeInformation.IsOSPlatform(OSPlatform.OSX);
 
         /// <summary>
         /// True iff running on FreeBSD </summary>
-        public static readonly bool FREE_BSD = RuntimeInformation.IsOSPlatform(OSPlatform.Create("FreeBSD"));
+        public static readonly bool FREE_BSD = RuntimeInformation.IsOSPlatform(OSPlatform.Create("FREEBSD"));
 
         // Possible Values: X86, X64, Arm, Arm64
         public static readonly string OS_ARCH = RuntimeInformation.OSArchitecture.ToString();
@@ -197,6 +197,8 @@ private static string GetFramework45PlusFromRegistry()
         // Checking the version using >= will enable forward compatibility.
         private static string CheckFor45PlusVersion(int releaseKey)
         {
+            if (releaseKey >= 533320)
+                return "4.8.1";
             if (releaseKey >= 460799)
                 return "4.8";
             if (releaseKey >= 460798)
@@ -241,4 +243,4 @@ private static string ExtractString(string input, Regex pattern)
             return (m.Groups.Count > 1) ? m.Groups[1].Value : string.Empty;
         }
     }
-}
+}