failOnVersionConflict has never been good for us. It is equivalent to
Maven dependencyConvergence which we discourage our users to use because
it is too tempermental and _creates_ version skew issues over time.
However, we had no real alternative for determining if our deps would be
misinterpeted by Maven.

failOnVersionConflict has been a constant drain and makes it really hard
to do seemingly-trivial upgrades. As evidenced by protobuf/build.gradle
in this change, it also caused _us_ to introduce a version downgrade.

This introduces our own custom requireUpperBoundDeps implementation so
that we can get back to simple dependency upgrades _and_ increase our
confidence in a consistent dependency tree.

The changes didn't introduce a bug. It is just we previously excluded
and re-defined errorprone with guava such that it would be closer to the
root and ended up beating protobuf-java-util's dep.

…ying on Guava's transitive dep