Declare FileReadTrapStreamWrapper::$context property

[staabm]

should fix warnings like

 Deprecated: Creation of dynamic property                                   
     PHPStan\Reflection\BetterReflection\SourceLocator\FileReadTrapStreamWrapper::$context is deprecated in                                              
     /home/runner/work/redaxo/redaxo/redaxo/src/core/lib/autoload.php on line       256                                                                        

this property is defined in the streamwrapper prototype and when missing creates a runtime warning

---

the fix is related to phpstan/phpstan#8610 but will not fix said issue

[phpstan-bot]

This pull request has been marked as ready for review.

[ondrejmirtes]

This needs a reproduction first. Here's an example how to reproduce open_basedir issues in an integration test: phpstan/phpstan#7518

[staabm]

I tried a lot of different things but the warning did not reproduce.

maybe this fix is obsolete with #2154.. lets see

[ondrejmirtes]

Well if you have a project where you see it, it should be easy to reduce the project to something small that still shows it.

[ondrejmirtes]

I expect #2154 to fix the problem, because there's just one reproducer -> one PR to fix it.