Add support for binding parameter with [FromBody] (#46641)

* Add support for binding parameter with [FromBody]

* Address feedback from review

Author: captainsafia

src/Http/Http.Extensions/gen/RequestDelegateGenerator.cs

@@ -69,7 +69,7 @@ public void Initialize(IncrementalGeneratorInitializationContext context)
                 },
                 (del, options, inferredMetadataResult) =>
                 {
-                    var handler = ({{endpoint.EmitHandlerDelegateType()}})del;
+                    var handler = ({{endpoint.EmitHandlerDelegateCast()}})del;
                     EndpointFilterDelegate? filteredInvocation = null;
 
                     if (options?.EndpointBuilder?.FilterFactories.Count > 0)