Consolidate XOnlyPubKey lookup hack

The places where we need to lookup information for a XOnlyPubKey
currently implement a hack which makes both serializations of the full
pubkey in order to try the CKeyIDs for the lookup functions. Instead of
duplicating this everywhere it is needed, we can consolidate the CKeyID
generation into a function, and then have wrappers around GetPubKey,
GetKey, and GetKeyOrigin which takes the XOnlyPubKey, retrieves all of
the CKeyIDs (using the new GetKeyIDs() function in XOnlyPubKey), and
tries their respective underlying lookup function.

src/pubkey.cpp

@@ -180,6 +180,23 @@ XOnlyPubKey::XOnlyPubKey(Span<const unsigned char> bytes)
     std::copy(bytes.begin(), bytes.end(), m_keydata.begin());
 }
 
+std::vector<CKeyID> XOnlyPubKey::GetKeyIDs() const
+{
+    std::vector<CKeyID> out;
+    // For now, use the old full pubkey-based key derivation logic. As it is indexed by
+    // Hash160(full pubkey), we need to return both a version prefixed with 0x02, and one
+    // with 0x03.
+    unsigned char b[33] = {0x02};
+    std::copy(m_keydata.begin(), m_keydata.end(), b + 1);
+    CPubKey fullpubkey;
+    fullpubkey.Set(b, b + 33);
+    out.push_back(fullpubkey.GetID());
+    b[0] = 0x03;
+    fullpubkey.Set(b, b + 33);
+    out.push_back(fullpubkey.GetID());
+    return out;
+}
+
 bool XOnlyPubKey::IsFullyValid() const
 {
     secp256k1_xonly_pubkey pubkey;