Fix Multiple Request for PHP (protocolbuffers#7008)

* Add scripts to test multirequest

* chmod ug+x multirequest.sh

* Add continuous test

* Compile c extension

* Class entry is obsolete in the second request
1) Needes to use class name in persistent map
2) Invalidate class entry stored in descriptor

* Add new files to dist

* Fix compile_extension

* Cleanup outputs for phpize

Add php 7.4 to docker image (protocolbuffers#6971) (protocolbuffers#6975

)

* Add php 7.4 to docker image

* Use https links

Update CHANGES.txt for 3.11.0 stable release (protocolbuffers#6944)

Remove add_proto_enumdesc and get_proto_enumdesc (protocolbuffers#6931)

Update CHANGES.txt with 3.11.0-RC1 release notes (protocolbuffers#6909)

Merge pull request protocolbuffers#6790 from protocolbuffers/rafi-kam…

…al-patch-4

Update CHANGES.txt for 3.10.1 release

Merge pull request protocolbuffers#6721 from protocolbuffers/rafi-kam…

…al-patch-1

Update CHANGES.txt with changes since 3.10.0-RC1

Update version to 3.9.2 (protocolbuffers#6682)

Merge pull request protocolbuffers#6621 from rafi-kamal/3.10.x-201909…

…051012

Update protobuf version for Java and PHP

Update protobuf version (protocolbuffers#6472)