added a HttpClientFactoryRestClientProvider to avoid having to expose a HttpClientFactoryRestClient.

src/Discord.Net.Rest/Net/HttpClientFactoryRestClientProvider.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Net.Http;
+
+namespace Discord.Net.Rest
+{
+    public static class HttpClientFactoryRestClientProvider
+    {
+
+        /// <exception cref="PlatformNotSupportedException">The default RestClientProvider is not supported on this platform.</exception>
+        public static RestClientProvider Create(HttpClient httpClient, bool useProxy = false)
+        {
+            return url =>
+            {
+                try
+                {
+                    return new HttpClientFactoryRestClient(url, httpClient, useProxy);
+                }
+                catch (PlatformNotSupportedException ex)
+                {
+                    throw new PlatformNotSupportedException("The default RestClientProvider is not supported on this platform.", ex);
+                }
+            };
+        }
+    }
+}