Change the "main" function in NonComposerComponentRegistration.php to closure to avoid naming conflicts.

[Hailong]

Description (*)

There is a function definition "main" in app/etc/NonComposerComponentRegistration.php, which is used by autoload. This change is to use a closure instead, to avoid naming conflicts.

Here is one scenario that the naming conflict happens:

1. I installed Magento 2.3 with composer as the document recommends:

   composer create-project --repository=https://repo.magento.com/ magento/project-community-edition <install-directory-name>
   

2. While later I need some new patches from the 2.3-develop branch, so I decided to change the Magento source to GitHub repository, my changes to the composer.json file looks like this:

   {
       "name": "magento/project-community-edition",
       ...
       "require": {
           ...
           "magento/magento2ce": "dev-2.3",
           ...
       },
       "replace": {
           "magento/magento2-base": "*"
       },
       ...
   }
   

   (There is also a change to the magento/magento2ce composer.json to add the "map arrays" accordingly)

3. Now since both the main project and magento/magento2ce would need to load the app/etc/NonComposerComponentRegistration.php, there will be an error says "Cannot redeclare ..."

Change the main function definition to closure would definitely resolve this issue.

Fixed Issues (if relevant)

N/A

Manual testing scenarios (*)

1. Create a Magento 2.3 project installation.
2. Update composer.json to reference Magento core code from GitHub repository.
3. Make sure the NonComposerComponentRegistration.php is loaded from both project directory and magento/magento2ce vendor package directory and no conflict during autoload process.

Contribution checklist (*)

• [* ] Pull request has a meaningful description of its purpose
• [* ] All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @Hailong. Thank you for your contribution
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[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @sidolov, thank you for the review.
ENGCOM-5159 has been created to process this Pull Request

[ghost]

@magento-cicd2 unfortunately, only members of the maintainers team are allowed to unassign developers from the pull request

[engcom-Foxtrot]

@magento run all tests

[m2-assistant]

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