Make library discovery context aware

Problem/Motivation

I created this issue because of https://www.drupal.org/project/gin_toolbar/issues/3293209#comment-15892466 🐛 Library information alter should not be context-aware Closed: outdated .

gin_toolbar injects css to the frontend but those css should be injected only if the user has the proper permissions to see the toolbar. I think there might be other ways of solving this but I liked the approach weblo's take on that linked comment where the library collector is context aware.

Proposed resolution

I think that something like that could never be part of a contrib module, but I wonder if `libraries` and `libraries-extend` cannot be made natively context aware.

Something like:

contexts:
  - user

Then if someone needs to extend the context of any library they current hooks or alterers can be used.