Fix InvokeFeatures.Set to bump revision for body-wrapping middleware

InvokeFeatures.Set<TFeature> was updating the feature dictionary without
incrementing _containerRevision. ASP.NET Core's FeatureReferences cache
uses Collection.Revision to detect feature swaps; without the bump, cached
feature references stay stale after middleware (e.g. OutputCache,
ResponseCompression) replaces a feature via HttpContext.Response.Body =
wrapper. The result was that response writes bypassed the wrapper entirely,
so OutputCache cached zero-byte bodies and subsequent cached responses
returned empty.

Resolves #1702.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: GarrettBeatty

.autover/changes/a0faddb0-c508-415c-b436-d99d68eafc56.json

@@ -0,0 +1,11 @@
+{
+  "Projects": [
+    {
+      "Name": "Amazon.Lambda.AspNetCoreServer",
+      "Type": "Patch",
+      "ChangelogMessages": [
+        "Fix InvokeFeatures.Set<TFeature> to bump the feature collection revision so middleware that wraps the response body (e.g. OutputCache, ResponseCompression) is properly visible to ASP.NET Core's FeatureReferences cache. Resolves https://github.com/aws/aws-lambda-dotnet/issues/1702 where IOutputCache stored empty response bodies."
+      ]
+    }
+  ]
+}

Libraries/src/Amazon.Lambda.AspNetCoreServer/Internal/InvokeFeatures.cs

@@ -117,10 +117,11 @@ public IEnumerator<KeyValuePair<Type, object>> GetEnumerator()
 
         public void Set<TFeature>(TFeature instance)
         {
-            if (instance == null)
-                return;
-
-            _features[typeof(TFeature)] = instance;
+            // Delegate to the indexer so _containerRevision is bumped, otherwise
+            // ASP.NET Core's FeatureReferences cache will return stale feature
+            // references after middleware (e.g. OutputCache, ResponseCompression)
+            // wraps the response body via HttpContext.Response.Body = wrapper.
+            this[typeof(TFeature)] = instance;
         }
 
         IEnumerator IEnumerable.GetEnumerator()