[PHP] Add declareStrictTypes option to AbstractPhpCodegen to generate declare(strict_types=1);

[Gosling-dude]

Summary

This PR introduces support for a new generator option: declareStrictTypes for PHP code generation.

When enabled via --additional-properties=declareStrictTypes=true, the generated PHP files will start with:

<?php
declare(strict_types=1);

This enforces strict typing in the generated PHP client code, promoting best practices for modern PHP development.

Affected Files

Codegen Core:

• AbstractPhpCodegen.java

  → Added support for the declareStrictTypes property and updated the help message.

• PHP Template Files:

Located in modules/openapi-generator/src/main/resources/php/

- model.mustache
- api.mustache
- api_test.mustache
- model_test.mustache

• Other templates starting with <?php

All updated to conditionally include:

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

Usage Example

To generate PHP code with declare(strict_types=1); included at the top of the files, run:

java -jar openapi-generator-cli.jar generate \
  -g php \
  --additional-properties=declareStrictTypes=true \
  -i https://raw.githubusercontent.com/OpenAPITools/openapi-generator/master/modules/openapi-generator/src/test/resources/3_0/petstore.yaml \
  -o /tmp/test-php

Then check any generated file (e.g., ApiClient.php) for:

<?php
declare(strict_types=1);

Fixes: #12771

Thank you for reviewing this contribution! 🙏

[wing328]

better do in the following way

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

to avoid blank lines

[Gosling-dude]

Sure, I'll do it.