'Strict deps' errors revolving around rules_scala bind rules

The `bind` actions in rules_scala `repositories` functions is mostly hidden from the user.
Meaning most users don't realize that if they want different versions of scala/junit/specs2 jars they need to override the bind actions.
When using `strict deps` in error mode this issue surfaces with the user not knowing what the problem is

Start with the rules_scala repositories functions and inspect how their bind actions select Scala, JUnit, and Specs2 jars. Reproduce the strict deps error mode behavior and determine what user-facing guidance or change is expected; done should make overriding those bindings and diagnosing the error clear.

Written by the indexing model from the issue text.