Down-integrate internal changes (#5467)

* Down-integrate internal changes

* Update generated code for php, objc and csharp.

* Add missing dependency in conformance_php
diff --git a/conformance/conformance_php.php b/conformance/conformance_php.php
index 799cc3e..cc6d4b9 100755
--- a/conformance/conformance_php.php
+++ b/conformance/conformance_php.php
@@ -3,6 +3,7 @@
 require_once("Conformance/WireFormat.php");
 require_once("Conformance/ConformanceResponse.php");
 require_once("Conformance/ConformanceRequest.php");
+require_once("Conformance/JspbEncodingConfig.php");
 require_once("Conformance/TestCategory.php");
 require_once("Protobuf_test_messages/Proto3/ForeignMessage.php");
 require_once("Protobuf_test_messages/Proto3/ForeignEnum.php");