Use include instead of forward declaration. (#2047)

Author: sbiscigl

aws-cpp-sdk-s3-crt/include/aws/s3-crt/S3CrtClient.h

@@ -8,6 +8,7 @@
 #include <aws/s3-crt/S3CrtErrors.h>
 #include <aws/core/client/AWSError.h>
 #include <aws/core/client/ClientConfiguration.h>
+#include <aws/core/auth/AWSCredentialsProviderChain.h>
 #include <aws/core/utils/crypto/Factories.h>
 #include <aws/s3-crt/ClientConfiguration.h>
 #include <aws/s3-crt/S3CrtErrorMarshaller.h>
@@ -110,7 +111,6 @@ namespace Aws
   {
     class AWSCredentials;
     class AWSCredentialsProvider;
-    class DefaultAWSCredentialsProviderChain;
   } // namespace Auth
 
   namespace S3Crt

code-generation/generator/src/main/resources/com/amazonaws/util/awsclientgenerator/velocity/cpp/s3/S3ClientHeader.vm

@@ -8,6 +8,7 @@
 \#include <aws/core/client/AWSError.h>
 \#include <aws/core/client/ClientConfiguration.h>
 #if($serviceNamespace == "S3Crt")
+\#include <aws/core/auth/AWSCredentialsProviderChain.h>
 \#include <aws/core/utils/crypto/Factories.h>
 \#include <aws/s3-crt/ClientConfiguration.h>
 \#include <aws/s3-crt/S3CrtErrorMarshaller.h>
@@ -63,9 +64,6 @@ namespace Aws
   {
     class AWSCredentials;
     class AWSCredentialsProvider;
-#if($serviceNamespace == "S3Crt")
-    class DefaultAWSCredentialsProviderChain;
-#end
   } // namespace Auth
 
   namespace ${metadata.namespace}