* Implement binary conformance test for oneof fields

* Update failure list

* Update failure list for php c extension

* Add binary conformance tests for map fields

* Update failure list

* Fix php conformance test

* Fix php conformance test

In 32-bit platform, int64 should be string. However, map iterator returns string key as integer.

* Add more test cases for map

* Update failure list

* Test singular fields are encoded in canonical way

* Defautl values in proto3 should not be encoded.
* Values should be converted to the canonical representation (e.g.,
long int64 value may be truncated for int32 field)

* Update failure list

* Update failure list

* Add conformance tests for explicit packed/unpacked fields

* Fix typo

* Update failure lists

* Update failure list

* Use enum class to make enum scoped

* Add binary conformance test for default repeated fields

1) Both packed and unpacked encoding should be accepted for parsing.
2) Encode should follow the default way for the syntax.

* Uncomment test

* Remove is_primitive

* Add failed tests to failure lists.

* Add failed test to failure list

* Use binary format to specify expected value

Text format cannot distinguish whether repeated field is packed or not.

* Change method name from ToHexString to ToOctString

* Add failed test to failure list

* Add failed test to php's failure list

* Fix comments

* Add binary conformance test case for bytes field

* Add failed conformance test to php's failure list

* Add conformance test for binary string

* Add failing tests to php failure list

* Change int64 json encoding to be string for php and ruby

* Fix ruby test

* Sync upb change

* Add a new conformance test for top level JSON null

* Fix field mask for php in json

* Update byte size

* Fix Any json encoding/decoding in php

* Fix comments

* Adopt upb change for timestamp and duration json to php

* Remove unused code

* Re-sync upb

* Fix php implementation timestamp json parsing

* Fix strptime use local timezone on mac.

* Remove succeeding tests

* Resync

* Add tests for values

* Fix php tests

* Fix encoder handlers change default value

Previously, oneofsubmsg_handler and submsg_handler change zval's default value directly.
The fix use REPLACE_ZVAL_VALUE which create a copy of parsed value and assign it to zval.

* Add missing reference to conformanc_test_impl.cc in Makefile

* Update conformance failure list

* Add conformance test for php c back

php c extension has different result for conformance test for different
php version and architecture. Try to add conformance back for php 7.1 c extension first.

* Disable conformance test for c extension on 32-bit architecture
32-bit and 64-bit have different failing tests

* Fix typo

* Enable ignoring unknown in json parsing in php

* Update generated descriptor files

* Update failure list for other languages.

* Remove unnecessary php files

* Add json encode/decode for php.

* Fix php conformance test on 32-bit machines.

* Fix conformance test for c extension.

* Fix comments