Merge bitcoin/bitcoin#30160: util: add BitSet

47f705b33f tests: add fuzz tests for BitSet (Pieter Wuille)
59a6df6bd5 util: add BitSet (Pieter Wuille)

Pull request description:

  Extracted from #30126.

  This introduces the `BitSet` data structure, inspired by `std::bitset`, but with a few features that cannot be implemented on top without efficiency loss:
  * Finding the first set bit (`First`)
  * Finding the last set bit (`Last`)
  * Iterating over all set bits (`begin` and `end`).

  And a few other operators/member functions that help readability for #30126:
  * `operator-` for set subtraction
  * `Overlaps()` for testing whether intersection is non-empty
  * `IsSupersetOf()` for testing (non-strict) supersetness
  * `IsSubsetOf()` for testing (non-strict) subsetness
  * `Fill()` to construct a set with all numbers from 0 to n-1, inclusive
  * `Singleton()` to construct a set with one specific element.

  Everything is tested through a simulation-based fuzz test that compares the behavior with normal `std::bitset` equivalent operations.

ACKs for top commit:
  instagibbs:
    ACK 47f705b33f
  achow101:
    ACK 47f705b33f
  cbergqvist:
    re-ACK 47f705b33f
  theStack:
    Code-review ACK 47f705b33f

Tree-SHA512: e451bf4b801f193239ee434b6b614f5a2ac7bb49c70af5aba24c2ac0c54acbef4672556800e4ac799ae835632bdba716209c5ca8c37433a6883dab4eb7cd67c1

test/sanitizer_suppressions/ubsan

@@ -58,6 +58,7 @@ unsigned-integer-overflow:TxConfirmStats::EstimateMedianVal
 unsigned-integer-overflow:prevector.h
 unsigned-integer-overflow:EvalScript
 unsigned-integer-overflow:xoroshiro128plusplus.h
+unsigned-integer-overflow:bitset_detail::PopCount
 implicit-integer-sign-change:CBlockPolicyEstimator::processBlockTx
 implicit-integer-sign-change:SetStdinEcho
 implicit-integer-sign-change:compressor.h