If, due to invalidation / reconsideration of blocks, the previous best header is no longer valid / guaranteed to be the most-work header in our block-index not known to be invalid, recalculate it.
Declared in <validation.h>
[[requires_capability(0x7f9513c48648), requires_capability(0x7f9502de9de8), requires_capability(0x7f950b21c5b8), requires_capability(0x7f9514bf65a8)]]
void
RecalculateBestHeader();