[TableGen][DecoderEmitter] Change SmallSetVector to SetVector (NFC) (#159108)

SmallSetVector is too optimistic, there are usually more than 16 unique
decoders and predicates. Modernize `typedef` to `using` while here.

Author: s-barannikov

llvm/utils/TableGen/DecoderEmitter.cpp

@@ -160,8 +160,8 @@ class LessEncodingIDByWidth {
   }
 };
 
-typedef SmallSetVector<CachedHashString, 16> PredicateSet;
-typedef SmallSetVector<CachedHashString, 16> DecoderSet;
+using PredicateSet = SetVector<CachedHashString>;
+using DecoderSet = SetVector<CachedHashString>;
 
 class DecoderTable {
 public:
@@ -274,7 +274,7 @@ class DecoderEmitter {
   void emitInstrLenTable(formatted_raw_ostream &OS,
                          ArrayRef<unsigned> InstrLen) const;
   void emitPredicateFunction(formatted_raw_ostream &OS,
-                             PredicateSet &Predicates) const;
+                             const PredicateSet &Predicates) const;
   void emitDecoderFunction(formatted_raw_ostream &OS,
                            const DecoderSet &Decoders,
                            unsigned BucketBitWidth) const;
@@ -838,8 +838,8 @@ void DecoderEmitter::emitInstrLenTable(formatted_raw_ostream &OS,
   OS << "};\n\n";
 }
 
-void DecoderEmitter::emitPredicateFunction(formatted_raw_ostream &OS,
-                                           PredicateSet &Predicates) const {
+void DecoderEmitter::emitPredicateFunction(
+    formatted_raw_ostream &OS, const PredicateSet &Predicates) const {
   // The predicate function is just a big switch statement based on the
   // input predicate index.
   OS << "static bool checkDecoderPredicate(unsigned Idx, const FeatureBitset "