Issue #3387637: The fake_site fixture should use a Composer-type repository

package_manager/src/ComposerInspector.php

package_manager/tests/fixtures/fake_site/composer.json

package_manager/tests/fixtures/fake_site/composer.lock

package_manager/tests/fixtures/fake_site/packages.json

...r/tests/fixtures/fake_site/vendor/composer/installed.json

...ules/fixture_manipulator/fixture_manipulator.services.yml

...ts/modules/fixture_manipulator/src/FixtureManipulator.php

.../tests/modules/fixture_manipulator/src/ProcessFactory.php

package_manager/tests/src/Kernel/ComposerInspectorTest.php

package_manager/tests/src/Kernel/FixtureManipulatorTest.php

scripts/PackageManagerFixtureCreator.php