IDEA-104500 Gradle: Allow to reuse common logic for other external systems

Use external system-provided library name for module-level libraries
Revert "[git] Fix equals & hashcode for GitRepoInfo"

This reverts commit b612a915b063e8c70069f9d38b2acf05c34399f7.
Better fix will follow
[git] Better fix of equals & hashcode for GitRepoInfo

We consider GitRepoInfos as equal if, in particular,
they have the same set of remotes, while the order of these remotes
in collection is not interesting.
(Remotes are (or may be) supplied as ArrayLists, while equals for the
ArrayList considers the order of the elements).

Use LinkedHashSet to preserve the original ordering,
but use the needed equality definition.