Update protobuf version for 3.19.4 (protocolbuffers#9449)

I also updated the PHP release notes in
php/ext/google/protobuf/package.xml.

Update protobuf version

Tweak wording of CHANGES.txt

Tweak wording in CHANGES.txt

Update protobuf version

Update protobuf version (protocolbuffers#9167)

Update protobuf version (protocolbuffers#9119)

Update version to 3.19.0-rc2 and fix changelog about Java 7 (protocol…

…buffers#9116)

* Update protobuf version

* Update CHANGES.txt to reflect that we're not yet dropping Java 7

Update PHP release notes for 3.19.0 (protocolbuffers#9110)

Update protobuf version to 3.18.1 (protocolbuffers#9051)

* Update protobuf version

* Update PHP release notes in package.xml