Fix GetHashCode with invariant mode

Signed-off-by: dotnet-bot-corefx-mirror <dotnet-bot@microsoft.com>

Author: tarekgh

src/Common/src/CoreLib/System/Globalization/CompareInfo.cs

@@ -1257,6 +1257,11 @@ internal int GetHashCodeOfString(string source, CompareOptions options)
                 throw new ArgumentException(SR.Argument_InvalidFlag, nameof(options));
             }
 
+            if (_invariantMode)
+            {
+                return ((options & CompareOptions.IgnoreCase) != 0) ? TextInfo.GetHashCodeOrdinalIgnoreCase(source) : source.GetHashCode();
+            }
+
             return GetHashCodeOfStringCore(source, options);
         }