If, due to invalidation / reconsideration of blocks, the previous best header is no longer valid / guaranteed to be the most-work header in our block-index not known to be invalid, recalculate it.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(0x7fd753e2f8c8), requires_capability(0x7fd74dcf0f78), requires_capability(0x7fd74a14eb78), requires_capability(0x7fd75e70fe08)]]
void
RecalculateBestHeader();