Adds a Pattern properties keyword to the v3.1 schema deserializer

Author: MaggieKimani1

src/Microsoft.OpenApi.Readers/V31/JsonSchemaDeserializer.cs

@@ -167,6 +167,12 @@ internal static partial class OpenApiV31Deserializer
                     o.Properties(n.CreateMap(LoadSchema));
                 }
             },
+            {
+                "patternProperties", (o, n) =>
+                {
+                    o.PatternProperties(n.CreateMap(LoadSchema));
+                }
+            },
             {
                 "additionalProperties", (o, n) =>
                 {

src/Microsoft.OpenApi/Models/OpenApiConstants.cs

@@ -400,6 +400,11 @@ public static class OpenApiConstants
         /// </summary>
         public const string Properties = "properties";
 
+        /// <summary>
+        /// Field: Pattern Properties
+        /// </summary>
+        public const string PatternProperties = "patternProperties";
+
         /// <summary>
         /// Field: AdditionalProperties
         /// </summary>