Change the return type of refreshIncremental so that implementations
can choose what the framework should do after the incremental refresh
regarding the index data files.
Move CoveringIndex.resolveConfig to IndexUtils.resolveColumns to make
it available to other index implementations.
What is the context for this pull request?
473
What changes were proposed in this pull request?
Does this PR introduce any user-facing change?
No
How was this patch tested?
With existing tests