[REQ][php] declareStrictTypes option for all PHP generators

[ybelenko]

Is your feature request related to a problem? Please describe.

Usually I totally against codegen options which modifies one line of code, but this one looks really handy.

Describe the solution you'd like

Add declareStrictTypes switch option to AbstractPhpCodegen class, then:

openapi-generator-cli generate -g php --additional-properties=declareStrictTypes=true \
    -o out -i petstore.yaml

then in all mustache files:

<?php 

{{#declareStrictTypes}}declare(strict_types=1);{{/declareStrictTypes}}

We also need to decide whether this switch option should be on or off by default. I think it should be on, but it can cause breaking changes.

Describe alternatives you've considered

Close this issue as not necessary feature 😆

Additional context

cc @jebentier @dkarlovi @mandrean @jfastnacht @renepardon

[SvenRtbg]

What about just adding strict types without offering an option? All supported PHP versions allow using them, and the only thing that is affected is the internal function calls within the generated code anyways: defining strict_types=1 does not at all affect calls from files not using strict types into the generated code, because that is exactly how strict types work.

[wing328]

What about just adding strict types without offering an option?

I don't mind adding strict types support without an option in the php-nextgen client generator.

Would you like to contribute a PR?

ref: #16480