In stat_exit we want to emit a final EVENT_HEAP_ALLOCATED for each cap
so that we get the same total allocation count as reported via +RTS -s.
To do so we need to update the per-cap total_allocated counts.

Previously we had a single calcAllocated(rtsBool) function that counted
the large allocations and optionally the nurseries for all caps. The GC
would always call it with false, and the stat_exit always with true.
The reason for these two modes is that the GC counts the nurseries via
clearNurseries() (which also updates the per-cap total_allocated
counts), so it's only the stat_exit() path that needs to count them.

We now split the calcAllocated() function into two: countLargeAllocated
and updateNurseriesStats. As the name suggests, the latter now updates
the per-cap total_allocated counts, in additon to returning a total.