This is a follow-up work to
SERVER-39085 that seeks to clarify the logic for selectively filtering and adding collation defaults to the provided index specs as well as determining which registration errors are ignorable.
Currently IndexBuildsCoordinator::_registerAndSetUpIndexBuild() bypasses both filtering and adding collation defaults on secondary. It may be feasible to bypass just the
addCollationDefaultsToIndexSpecsForCreate() call alone.
There is also a potential improvement for _registerAndSetUpIndexBuild() to return early rather than wait for IndexBuildsManager::setUpIndexBuild() to fail and check its result for ignorable errors.
This may allow up to skip some of the registration and setup and makes it clearer that secondary oplog application will ignore index inconsistency across replica set members.