The checkpoint code currently re-parses configuration strings for some configuration options, it would make sense to do a single configuration string parsing phase, and populate a structure which can be passed around instead.

One case of re-parsing is when individual btrees need to extract configuration information they pull it from strings - it would be nice to only do that string parsing once - but doing so will mean passing a context object through apply function(s).

Once we have such a checkpoint context object around, I think we should be able to move some content from the WT_CONNECTION handle into it as well.