[php-mezzio-ph] PHP 8 support

[Articus]

Huge update for php-mezzio-ph generator:

• minimal PHP version bump to 7,3 - PHP 7.2 end of life #9200
• proper support for container data type - multidimensional arrays and maps are handled correctly now
• custom CLI option "modern" to generate code using modern language syntax for PHP 8 projects
• support for referenced query parameters and referenced query parameter schemas
• removal of obsolete samples folder samples/openapi3/server/petstore/php-mezzio-ph

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master, 5.1.x, 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

cc @jebentier @dkarlovi @mandrean @jfastnacht @ackintosh @ybelenko @renepardon

[wing328]

Tested locally and can start a server without issues

$ php -S 0.0.0.0:8080 -t ./public
[Fri May 21 14:38:31 2021] PHP 7.4.3 Development Server (http://0.0.0.0:8080) started

[wing328]

Some users may consider this as a breaking change and we may add a php-mezzio-ph-deprecated generator to keep them happy.

[Articus]

Thought about that :) But I believe it should be done next year after PHP 8.1 release. Currently there are three supported versions of PHP - 7.3 , 7.4 , 8.0 . By default (without modern option) php-mezzio-ph generates code that is compatible with them all (and even with 7.1 and 7.2 that are no longer supported). With modern option generated code heavily uses new features introduced in 8.0 and can no longer run on 7.* . So right now full PHP 8 support is an optional feature, not a breaking change.

[ybelenko]

Some users may consider this as a breaking change and we may add a php-mezzio-ph-deprecated generator to keep them happy.

It's hard to say what we can consider breaking changes in server codegens. If I remember correct @jimschubert thinks that server generators cannot cause breaking changes at all because users generate fresh stubs during migration anyway.

[ybelenko]

@Articus thanks for clarifications I wasn't focused enough, didn't notice you've added two generators. That's not common codegen flow.