Dynamically copy scaffold file mapping when create fake_site fixture

Opened #3340355: [PP-1] Add support for scaffold files that aren't defined by Drupal core or the root composer.json as a follow-up here.

Given that the scope of this issue, per discussion with @tedbow, only involves the file mapping from drupal/core and the root composer.json, I think it's probably okay if someone who isn't me deals with this.

Did you try running it locally? The creator of the fixture itself does not have tests, so a green test run is meaningless!

$ composer create-site-fixture ~/core
> \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture
Script \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture handling the create-site-fixture event terminated with an exception

In ComposerFixtureCreator.php line 39:
                                                                                                                                                                                 
  file_get_contents(/Users/wim.leers/core/modules/contrib/automatic_updates/scripts/src/../../package_manager/tests/fixtures/fake_site../path_repos/drupal--core/composer.json)  
  : Failed to open stream: No such file or directory                                                                                                                             
                                                                                                                                                                                 

create-site-fixture [--dev] [--no-dev] [--] [<args>...]

And if I fix that I get

$ composer create-site-fixture ~/core
> \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture
Script \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture handling the create-site-fixture event terminated with an exception

In ComposerFixtureCreator.php line 41:
                                         
  Undefined array key "drupal-scaffold"  
                                         

create-site-fixture [--dev] [--no-dev] [--] [<args>...]

If I run it locally I get

$ composer create-site-fixture ../../../core
> \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture
Script \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture handling the create-site-fixture event terminated with an exception

In ComposerFixtureCreator.php line 39:
                                                                               
  file_get_contents(/Users/kunal.sachdev/www/d9-autoupdates/modules/contrib/a  
  utomatic_updates/scripts/src/../../package_manager/tests/fixtures/fake_site  
  ../path_repos/drupal--core/composer.json): Failed to open stream: No such f  
  ile or directory                                                             
                                                                               

create-site-fixture [--dev] [--no-dev] [--] [<args>...]

And if I fix that I get

$ composer create-site-fixture ../../../core
> \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture

Fixture created 🎉.% 

And I also checked the scaffold file mappings, it had copied correct scaffold file mappings.

composer create-site-fixture ~/core

was wrong of me!

I should've done

$ composer create-site-fixture ~/core/core
> \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture

Fixture created 🎉.

I can confirm this works correctly. But what's missing is actually including the results of executing that command in this MR! 😅

1. Changes look good. 👍
2. Manual test:
   

   curl https://git.drupalcode.org/project/automatic_updates/-/merge_requests/701.diff | git apply -3v
   

   $ rm -rf package_manager/tests/fixtures/fake_site/composer.lock 
   wim.leers at MacBookPro-WimLeers in ~/core/modules/contrib/automatic_updates on 3.0.x*
   $ composer create-site-fixture /Users/wim.leers/core/core
   > \Drupal\automatic_updates\Development\ComposerFixtureCreator::createFixture
   
   Fixture created 🎉.
   wim.leers at MacBookPro-WimLeers in ~/core/modules/contrib/automatic_updates on 3.0.x*
   $ git diff
   wim.leers at MacBookPro-WimLeers in ~/core/modules/contrib/automatic_updates on 3.0.x*
   

   ⇒ 🚀

Like! Over and out.