* Down integrate to GitHub

* Remove unintentional double assign

* Change ByteCountInt64 to int64_t

* Revert changes in binary_conformance_test.cc

* Revert unnecessary changes

Remove duplicate entry in third party list

* Implement binary conformance test for oneof fields

* Update failure list

* Update failure list for php c extension

On the linked Wiki page, it can be seen that the creator is `opticron`, whose Github repository is also linked, and contains a more up-to-date implementation.

Linakge Monitor fix to handle a new version of protobuf-bom not available in Maven Central

* Sync upb

https://github.com/protocolbuffers/upb/pull/209

* Update upb

https://github.com/protocolbuffers/upb/pull/210

- use final instead of obvious types for local variables
- add missing `void` return type
- make the comments doccomments (///)

This adds links under the Clojure header to

https://protojure.github.ioSigned-off-by: Greg Haskins <gregory.haskins@gmail.com>

* 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

* introduce GOOGLE_PROTOBUF_SUPPORT_SYSTEM_MEMORY

* allow building net45 target on unix systems too

* add Span<> support on net45 as well

Document proto2 feature implementations in Google.Protobuf

C# Proto2 feature : Finale

Reworded info about message initialization

Addressed review comments

Java: Add Automatic-Module-Name entries to the Manifest

This commit removes the question template. It also updates the bug report and feature request templates to direct questions to the mailing list.

* When length is zero, substr returns null instead of emptry string, which breaks the invariable for message.
* Tested in https://github.com/protocolbuffers/protobuf/pull/6560

Update version number

* For missing message value, map should create a default message
instance in order to keep its invariable.
* On 32-bit platform, int64 map key should be string

We've notice significant issues downloading from zlib.net. Since there
are already other archives coming from GitHub, this shouldn't negatively
affect reliability.

Optimization for layout_init()

* Add missing files under benchmarks/ to the dist

* fix typo

* Sync upb

* https://github.com/protocolbuffers/upb/pull/208

* Fix php c extension compiling

Don't use macros defined by upb

* Update ruby conformance failure list

Enums use varint, so if the value is negative it should end up being longer.

This was caught my new conformance test cases.