CollectionBulkLoader does not anticipate exceptions from MultiIndexBlock

Currently, CollectionBulkLoaderImpl uses CollectionBulkLoaderImpl::_runTaskReleaseResourcesOnFailure() to wrap function calls into other components such as the MultiIndexBlock index builder component. CollectionBulkLoaderImpl::_runTaskReleaseResourcesOnFailure() assumes no exceptions will reach its top level, since it catches all exceptions and immediately calls std::terminate() when they are caught.

Since some MultiIndexBlock functions can uassert, I believe we ought to convert exceptions into Statuses either in CollectionBulkLoaderImpl at its call sites, or within the MultiIndexBlock functions themselves.