Add a hashCode field to the diagnostics object to keep track of the hash value

Author: MaggieKimani1

src/Microsoft.OpenApi.Readers/OpenApiDiagnostic.cs

@@ -26,5 +26,10 @@ public class OpenApiDiagnostic : IDiagnostic
         /// Open API specification version of the document parsed.
         /// </summary>
         public OpenApiSpecVersion SpecificationVersion { get; set; }
+
+        /// <summary>
+        /// The unique hash code of the generated OpenAPI document
+        /// </summary>
+        public int HashCode { get; set; }
     }
 }

src/Microsoft.OpenApi.Readers/ParsingContext.cs

@@ -75,6 +75,7 @@ internal OpenApiDocument Parse(YamlDocument yamlDocument)
                     throw new OpenApiUnsupportedSpecVersionException(inputVersion);
             }
 
+            Diagnostic.HashCode = doc.GetHashCode();
             return doc;
         }