Previously, it only folded begin/end access into a single runtime
operation. When all accessed for a uniquely identified storage object
have been folded, then they can all be removed.
Reworked the design of the pass so this falls out naturally just by
updating AccessedStorageAnalysis.
Use AccessedStorageAnalysis to find access markers with no nested conflicts.
This optimization analyzes the scope of each access to determine
whether it contains a potentially conflicting access. If not, then it
can be demoted to an instantaneous check, which still catches
conflicts on any enclosing outer scope.
This removes up to half of the runtime calls associated with
exclusivity checking.
