keep options.KeyTransformer working and support new style.

Author: catcherwong

Enyim.Caching/Configuration/MemcachedClientConfiguration.cs

@@ -122,6 +122,11 @@ public MemcachedClientConfiguration(
                     _logger.LogError(new EventId(), ex, $"Unable to load '{options.KeyTransformer}' KeyTransformer");
                 }
             }
+            else if (keyTransformer != null)
+            {
+                this._keyTransformer = keyTransformer;
+                _logger.LogDebug($"Use KeyTransformer Type : '{keyTransformer.ToString()}'");
+            }
 
             if (NodeLocator == null)
             {

Enyim.Caching/EnyimMemcachedServiceCollectionExtensions.cs

@@ -47,6 +47,7 @@ private static IServiceCollection AddEnyimMemcached(IServiceCollection services,
             configure(services);
 
             services.TryAddSingleton<ITranscoder, DefaultTranscoder>();
+            services.TryAddSingleton<IMemcachedKeyTransformer, DefaultKeyTransformer>();
             services.TryAddTransient<IMemcachedClientConfiguration, MemcachedClientConfiguration>();
             services.AddSingleton<MemcachedClient, MemcachedClient>();