Return the script type from Solver

Because false is synonymous with TX_NONSTANDARD, this conveys the same
information and makes the handling explicitly based on script type,
simplifying each call site.

Prior to this change it was common for the return value to be ignored,
or for the return value and TX_NONSTANDARD to be redundantly handled.

src/core_write.cpp

@@ -141,8 +141,7 @@ void ScriptToUniv(const CScript& script, UniValue& out, bool include_address)
     out.pushKV("hex", HexStr(script.begin(), script.end()));
 
     std::vector<std::vector<unsigned char>> solns;
-    txnouttype type;
-    Solver(script, type, solns);
+    txnouttype type = Solver(script, solns);
     out.pushKV("type", GetTxnOutputType(type));
 
     CTxDestination address;