If, due to invalidation / reconsideration of blocks, the previous best header is no longer valid / guaranteed to be the most-work header in our block-index not known to be invalid, recalculate it.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(0x7fbc8fcf9e28), requires_capability(0x7fbc96d925e8), requires_capability(0x7fbcaf728058), requires_capability(0x7fbc9e23f738)]]
void
RecalculateBestHeader();