fix: visibility of extension methods

Author: baywet

src/Microsoft.OpenApi/Extensions/OpenApiReferencableExtensions.cs

@@ -10,12 +10,12 @@ namespace Microsoft.OpenApi
     /// <summary>
     /// Extension methods for resolving references on <see cref="IOpenApiReferenceable"/> elements.
     /// </summary>
-    public static class OpenApiReferenceableExtensions
+    internal static class OpenApiReferenceableExtensions
     {
         /// <summary>
         /// Resolves a JSON Pointer with respect to an element, returning the referenced element.
         /// </summary>
-        /// <param name="element">The referencable Open API element on which to apply the JSON pointer</param>
+        /// <param name="element">The referenceable Open API element on which to apply the JSON pointer</param>
         /// <param name="pointer">a JSON Pointer [RFC 6901](https://tools.ietf.org/html/rfc6901).</param>
         /// <returns>The element pointed to by the JSON pointer.</returns>
         public static IOpenApiReferenceable ResolveReference(this IOpenApiReferenceable element, JsonPointer pointer)

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -1066,10 +1066,6 @@ namespace Microsoft.OpenApi
         protected override void SerializeAdditionalV31Properties(Microsoft.OpenApi.IOpenApiWriter writer) { }
         protected override void SetAdditional31MetadataFromMapNode(System.Text.Json.Nodes.JsonObject jsonObject) { }
     }
-    public static class OpenApiReferenceableExtensions
-    {
-        public static Microsoft.OpenApi.IOpenApiReferenceable ResolveReference(this Microsoft.OpenApi.IOpenApiReferenceable element, Microsoft.OpenApi.JsonPointer pointer) { }
-    }
     public class OpenApiRequestBody : Microsoft.OpenApi.IOpenApiDescribedElement, Microsoft.OpenApi.IOpenApiElement, Microsoft.OpenApi.IOpenApiExtensible, Microsoft.OpenApi.IOpenApiReadOnlyExtensible, Microsoft.OpenApi.IOpenApiReferenceable, Microsoft.OpenApi.IOpenApiRequestBody, Microsoft.OpenApi.IOpenApiSerializable, Microsoft.OpenApi.IShallowCopyable<Microsoft.OpenApi.IOpenApiRequestBody>
     {
         public OpenApiRequestBody() { }