Calculate the amount of disk space the block & undo files currently use
Declared in <node/blockstorage.h>
[[requires_capability(0x7f95130c9698), requires_capability(0x7f950163c988), requires_capability(0x7f95241d9978), requires_capability(0x7f951f330c78), requires_capability(0x7f950b9c2c38), requires_capability(0x7f95175c5388)]]
uint64_t
CalculateCurrentUsage();The total size in bytes of the block and undo files on disk.