feat: Improve the requirement checker detection

[theofidry]

• Leverage a new class RequirementsBuilder to facilitate the collection of the requirements, making the collecting code more readable.
• Add unique checks and sorting to the builder to stabilize the output
• Fix the computed requirements when both the composer.json and composer.lock are found

This PR is not ideal in the sense that it combines a refactoring with an improvement and a fix, but unfortunately the offending code is too hard to deal with to make it worth to split the work any further.