Merge bitcoin/bitcoin#25664: refactor: Redefine IsSolvable() using descriptors

b16f93cadd script/sign: remove needless IsSolvable() utility (Antoine Poinsot)
c232ef20c0 outputtype: remove redundant check for uncompressed keys in AddAndGetDestinationForScript (Antoine Poinsot)

Pull request description:

  Now that we have descriptors there is no need to try to sign for a scriptPubKey using dummy signatures, and using a mocked verification of this witness against the interpreter, just to make sure we know how to spend such a Script. Just try to infer a solvable descriptor: any scriptPubKey that we can sign for can be inferred as such.

  This came up in #24149 but i think it's worth it on its own.

ACKs for top commit:
  instagibbs:
    ACK b16f93cadd
  achow101:
    re-ACK b16f93cadd
  furszy:
    ACK b16f93ca, only change is the `IsSolvable` helper function removal.

Tree-SHA512: 137068157ce90210b710b1bf9ac3c400e2ff5af1112f892094b69875ea473d6a899f52adb51e5030cb907dee517602059cd1661107808558efa5de842ba12b41

src/wallet/scriptpubkeyman.cpp

@@ -1456,7 +1456,8 @@ void LegacyScriptPubKeyMan::LearnRelatedScripts(const CPubKey& key, OutputType t
         CTxDestination witdest = WitnessV0KeyHash(key.GetID());
         CScript witprog = GetScriptForDestination(witdest);
         // Make sure the resulting program is solvable.
-        assert(IsSolvable(*this, witprog));
+        const auto desc = InferDescriptor(witprog, *this);
+        assert(desc && desc->IsSolvable());
         AddCScript(witprog);
     }
 }