This PR fixes #1335 by keeping track of versions of provided dependencies and keeping only those providers that actually satisfy the package and version dependencies.

I've also reworked and split the functions into several smaller ones and documented the control flow of the main function as much as possible (it was very difficult to understand at first what the original function was doing, so I tried my best to make it as easily understandable for future maintainers as I could).

P.S. I'm very new to alpm, so I couldn't find an alpm function that checks if a package satisfies a dependency. If one exists, we can use it instead.