Fix php well known type conformance tests (#3828)

* Fix php well known type conformance tests

* Properly generate code for test.proto

* Provide GPBMetadata files in c extensions for generated files to import.

* Remove unnecessary test

* Clean up code

* Add declaration for initOnce.

* Refactoring
diff --git a/conformance/conformance_php.php b/conformance/conformance_php.php
index 4dc18f5..19f9a09 100755
--- a/conformance/conformance_php.php
+++ b/conformance/conformance_php.php
@@ -3,24 +3,6 @@
 require_once("Conformance/WireFormat.php");
 require_once("Conformance/ConformanceResponse.php");
 require_once("Conformance/ConformanceRequest.php");
-require_once("Google/Protobuf/Any.php");
-require_once("Google/Protobuf/Duration.php");
-require_once("Google/Protobuf/FieldMask.php");
-require_once("Google/Protobuf/Struct.php");
-require_once("Google/Protobuf/Value.php");
-require_once("Google/Protobuf/ListValue.php");
-require_once("Google/Protobuf/NullValue.php");
-require_once("Google/Protobuf/Timestamp.php");
-require_once("Google/Protobuf/DoubleValue.php");
-require_once("Google/Protobuf/BytesValue.php");
-require_once("Google/Protobuf/FloatValue.php");
-require_once("Google/Protobuf/Int64Value.php");
-require_once("Google/Protobuf/UInt32Value.php");
-require_once("Google/Protobuf/BoolValue.php");
-require_once("Google/Protobuf/DoubleValue.php");
-require_once("Google/Protobuf/Int32Value.php");
-require_once("Google/Protobuf/StringValue.php");
-require_once("Google/Protobuf/UInt64Value.php");
 require_once("Protobuf_test_messages/Proto3/ForeignMessage.php");
 require_once("Protobuf_test_messages/Proto3/ForeignEnum.php");
 require_once("Protobuf_test_messages/Proto3/TestAllTypesProto3.php");
@@ -28,12 +10,6 @@
 require_once("Protobuf_test_messages/Proto3/TestAllTypesProto3_NestedEnum.php");
 
 require_once("GPBMetadata/Conformance.php");
-require_once("GPBMetadata/Google/Protobuf/Any.php");
-require_once("GPBMetadata/Google/Protobuf/Duration.php");
-require_once("GPBMetadata/Google/Protobuf/FieldMask.php");
-require_once("GPBMetadata/Google/Protobuf/Struct.php");
-require_once("GPBMetadata/Google/Protobuf/Timestamp.php");
-require_once("GPBMetadata/Google/Protobuf/Wrappers.php");
 require_once("GPBMetadata/Google/Protobuf/TestMessagesProto3.php");
 
 use  \Conformance\WireFormat;
@@ -78,7 +54,12 @@
     } elseif ($request->getRequestedOutputFormat() == WireFormat::PROTOBUF) {
       $response->setProtobufPayload($test_message->serializeToString());
     } elseif ($request->getRequestedOutputFormat() == WireFormat::JSON) {
-      $response->setJsonPayload($test_message->serializeToJsonString());
+      try {
+          $response->setJsonPayload($test_message->serializeToJsonString());
+      } catch (Exception $e) {
+          $response->setSerializeError($e->getMessage());
+          return $response;
+      }
     }
 
     return $response;