Add hook_requirements check that PHP storage is writeable

Problem/Motivation

📌 Deprecate trigger_error in FileStorage::createDirectory() to allow replacing calls to :::expectWarning*() in Drupal\Tests\Component\PhpStorage\FileStorageTest RTBC previously raised a PHP language warning if creating a directory failed, but there are other ways that PHP storage could fail (disk full, permissions, etc) when the directory exists, and these currently fail silently because TwigPhpStorageCache::write() does not check the return code of FileStorage::save().

Steps to reproduce

Proposed resolution

Add a hook_requirements() that writes a dummy file to PHP storage and ensures there is no error.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet