[Runtime] Make project_dir configurable

[wickedOne]

Q	A
Branch?	7.4
Bug fix?	no
New feature?	yes
Deprecations?	no
Issues	Fix #59954
License	MIT

this would allow a composer.json file at /alternative/location/composer.json be configured with

  "extra": {
    "runtime": {
      "project_dir": "/../../"
    }
  }

while using

COMPOSER=/alternative/location/composer.json composer update

generate a autoload_runtime.php with the following project_dir

$runtime = new $runtime(($_SERVER['APP_RUNTIME_OPTIONS'] ?? $_ENV['APP_RUNTIME_OPTIONS'] ?? []) + [
  'project_dir' => dirname(__DIR__, 1),
]);

i did not meddle with the autoload template discovery as that's currently already configurable and would introduce a bc break. also it makes sense in a way that every config value is relative to the composer.json file itself

[nicolas-grekas]

Can this be tested?
Note that this should target 7.3 as it's an improvement, not a butfix

[wickedOne]

Can this be tested?

i'm not entirely sure as the plugin uses a lot of built in functions with regards to directory / file locations and a static method to retrieve a composer config.... would you guys even be open to have a dev depdency like vfsStream?

Note that this should target 7.3 as it's an improvement, not a bugfix

check

[nicolas-grekas]

Thank you @wickedOne.