[resolver] Use `resolvelib` for the dependency resolution

[webknjaz]

I'm raising this because the issue search hasn't brought up any related discussions. I noticed that micropip uses a very simple homegrown resolution process and would probably be less stable than the widely used one. Pip's current backtracking resolver is a pluggable and agnostic. It can be brought into other projects easily (I integrated it into ansible-galaxy, for example). It's called resolvelib and it can be a dependency (or vendored). The project is here: https://github.com/sarugaku/resolvelib.