Add support for pattern properties

# Conflicts:
#	src/Microsoft.OpenApi/Models/OpenApiSchema.cs

Author: MaggieKimani1

src/Microsoft.OpenApi/Models/OpenApiSchema.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. 
 
 using System;
@@ -227,6 +227,15 @@ public class OpenApiSchema : IOpenApiExtensible, IOpenApiReferenceable, IOpenApi
         /// </summary>
         public IDictionary<string, OpenApiSchema> Properties { get; set; } = new Dictionary<string, OpenApiSchema>();
 
+        /// <summary>
+        /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
+        /// PatternProperty definitions MUST be a Schema Object and not a standard JSON Schema (inline or referenced)
+        /// Each property name of this object SHOULD be a valid regular expression according to the ECMA 262 r
+        /// egular expression dialect. Each property value of this object MUST be an object, and each object MUST 
+        /// be a valid Schema Object not a standard JSON Schema.
+        /// </summary>
+        public IDictionary<string, OpenApiSchema> PatternProperties { get; set; } = new Dictionary<string, OpenApiSchema>();
+
         /// <summary>
         /// Follow JSON Schema definition: https://tools.ietf.org/html/draft-fge-json-schema-validation-00
         /// </summary>
@@ -363,11 +372,12 @@ public OpenApiSchema(OpenApiSchema schema)
             MinItems = schema?.MinItems ?? MinItems;
             UniqueItems = schema?.UniqueItems ?? UniqueItems;
             Properties = schema?.Properties != null ? new Dictionary<string, OpenApiSchema>(schema.Properties) : null;
+            PatternProperties = schema?.PatternProperties != null ? new Dictionary<string, OpenApiSchema>(schema.PatternProperties) : null;
             MaxProperties = schema?.MaxProperties ?? MaxProperties;
             MinProperties = schema?.MinProperties ?? MinProperties;
             AdditionalPropertiesAllowed = schema?.AdditionalPropertiesAllowed ?? AdditionalPropertiesAllowed;
             AdditionalProperties = schema?.AdditionalProperties != null ? new(schema?.AdditionalProperties) : null;
-            Discriminator = schema?.Discriminator != null ? new(schema?.Discriminator) : null;
+            Discriminator = schema?.Discriminator != null ? new(schema?.Discriminator) : null; 
             Example = schema?.Example != null ? new(schema?.Example.Node) : null;
             Examples = schema?.Examples != null ? new List<JsonNode>(schema.Examples) : null;
             Enum = schema?.Enum != null ? new List<JsonNode>(schema.Enum) : null;
@@ -596,6 +606,7 @@ internal void WriteV31Properties(IOpenApiWriter writer)
             writer.WriteProperty(OpenApiConstants.V31ExclusiveMinimum, V31ExclusiveMinimum);            
             writer.WriteProperty(OpenApiConstants.UnevaluatedProperties, UnevaluatedProperties, false);
             writer.WriteOptionalCollection(OpenApiConstants.Examples, Examples, (nodeWriter, s) => nodeWriter.WriteAny(new OpenApiAny(s)));
+            writer.WriteOptionalMap(OpenApiConstants.PatternProperties, PatternProperties, (w, s) => s.SerializeAsV31(w));
         }
 
         /// <summary>

src/Microsoft.OpenApi/Reader/V31/OpenApiSchemaDeserializer.cs

@@ -150,6 +150,10 @@ internal static partial class OpenApiV31Deserializer
                 "properties",
                 (o, n, t) => o.Properties = n.CreateMap(LoadOpenApiSchema, t)
             },
+            {
+                "patternProperties",
+                (o, n, t) => o.PatternProperties = n.CreateMap(LoadOpenApiSchema, t)
+            },
             {
                 "additionalProperties", (o, n, _) =>
                 {