scripted-diff: Use std::span over Span

-BEGIN VERIFY SCRIPT-

 ren() { sed -i "s!\<$1\>!$2!g" $( git grep -l "$1" -- "./src" ":(exclude)src/span.h" ":(exclude)src/leveldb/db/log_test.cc" ) ; }

 ren Span            std::span
 ren AsBytes         std::as_bytes
 ren AsWritableBytes std::as_writable_bytes

 sed -i 's!SpanPopBack(Span!SpanPopBack(std::span!g' ./src/span.h

-END VERIFY SCRIPT-

src/policy/policy.cpp

@@ -281,7 +281,7 @@ bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
         // - No annexes
         if (witnessversion == 1 && witnessprogram.size() == WITNESS_V1_TAPROOT_SIZE && !p2sh) {
             // Taproot spend (non-P2SH-wrapped, version 1, witness program size 32; see BIP 341)
-            Span stack{tx.vin[i].scriptWitness.stack};
+            std::span stack{tx.vin[i].scriptWitness.stack};
             if (stack.size() >= 2 && !stack.back().empty() && stack.back()[0] == ANNEX_TAG) {
                 // Annexes are nonstandard as long as no semantics are defined for them.
                 return false;