Create package_manager validator to ensure the project to be installed is not already installed by Composer

Problem/Motivation

Follow up to #3245770: Create a service to composer install via package_manager from Automatic Updates

Project Browser will probably filter out modules that have already been installed. But in the case that the browser presents a project that is not installed and before the "Download" button clicked it is possible the project may have installed by another user.

Proposed resolution

Implement a listener to that listens to most of the Pre*Events for package_manager and ensure the project doesn't already exist in the project. Throw an error if the project is present.

Remaining tasks

• ✅ File an issue about this project
• ☐ Addition/Change/Update/Fix to this project
• ☐ Testing to ensure no regression
• ☐ Automated unit/functional testing coverage
• ☐ Developer Documentation support on feature change/addition
• ☐ User Guide Documentation support on feature change/addition
• ☐ Code review from 1 Drupal core team member
• ☐ Full testing and approval
• ☐ Credit contributors
• ☐ Review with the product owner
• ☐ Release

User interface changes

API changes

Data model changes

Release notes snippet