Merge bitcoin/bitcoin#32490: refactor: Remove UB in prevector reverse iterators

faf9082a5f test: Fix whitespace in prevector_tests.cpp (MarcoFalke)
fa7f04c8a7 refactor: Remove UB in prevector reverse iterators (MarcoFalke)

Pull request description:

  `rend()` creates a pointer with offset `-1`. This is UB, according to the C++ standard: https://eel.is/c++draft/expr.add#4:

      When an expression J that has integral type is added to [...] an
      expression P of pointer type, the result has the type of P.

      ... if P points to a (possibly-hypothetical) array element i of an
      array object x with n elements [...] the expressions P + J and J + P
      (where J has the value j) point to the (possibly-hypothetical) array
      element i+j of x if 0≤i+j≤n [...]

      Otherwise, the behavior is undefined.

  Also, it is unclear why the functions exist at all, when stdlib utils such as `std::reverse_iterator{it}` or `std::views::reverse` can be used out of the box.

  So remove them, along with the ubsan suppressions, that are no longer used.

  I've tagged this a refactor, because the code was always dead (unused outside of tests). And since commit 2925bd537c it was completely dead. Also, I could not find a sanitizer that detects this type of UB.

ACKs for top commit:
  l0rinc:
    tested ACK faf9082a5f
  achow101:
    ACK faf9082a5f
  stickies-v:
    ACK faf9082a5f, nice find.
  theuni:
    utACK faf9082a5f

Tree-SHA512: 31511d520a1c0fdd65c2e5f1a8ef6fd17464303b6bff88a5d9d9577adfee849d431deb510882b6f4e15e8fb7168861bc0d26fca3bed4278f57a9d6e7b1235dce

test/sanitizer_suppressions/ubsan

@@ -54,7 +54,6 @@ unsigned-integer-overflow:DecompressAmount
 unsigned-integer-overflow:crypto/
 unsigned-integer-overflow:MurmurHash3
 unsigned-integer-overflow:TxConfirmStats::EstimateMedianVal
-unsigned-integer-overflow:prevector.h
 unsigned-integer-overflow:InsecureRandomContext::rand64
 unsigned-integer-overflow:InsecureRandomContext::SplitMix64
 unsigned-integer-overflow:bitset_detail::PopCount
@@ -62,7 +61,6 @@ implicit-integer-sign-change:SetStdinEcho
 implicit-integer-sign-change:compressor.h
 implicit-integer-sign-change:crypto/
 implicit-integer-sign-change:TxConfirmStats::removeTx
-implicit-integer-sign-change:prevector.h
 implicit-integer-sign-change:verify_flags
 implicit-integer-sign-change:EvalScript
 implicit-integer-sign-change:serialize.h