Similar to the TransportVersions holder class, IndexVersions is the new
place to contain all constants for IndexVersion. This commit moves all
existing constants to the new class. It is purely mechanical.
* Replaced some occurrences of Version.CURRENT toString
* Added unit tests for the 2 different warn header patterns in HeaderWarnings
* Comment to clarify non-semantic versions + revert change on Version.major message
Re-applies the changes from #99572 to move some bwc tests to a junit-based build infrastructure. Some tests that did not handle the move well have been kept in rolling-upgrade-legacy using the old gradle-based infrastructure
Two test suites did not react well to the junit-based bwc infrastructure, so those have been separated into a legacy module using the old gradle-based system until they can be looked at properly.
This unblocks the 8.11 release.
Ryan Ernst
Mark Vieira
Lorenzo Dematté
Simon Cooper