[test] libSyntax: add a flag to swift-syntax-test to print trivial node kinds.

These trivial node kinds include node collections like stmtlist and
unknown syntax like UnknownExpr.

include/swift/Syntax/RawSyntax.h

@@ -188,6 +188,7 @@ enum class SourcePresence {
 struct SyntaxPrintOptions {
   bool Visual = false;
   bool PrintSyntaxKind = false;
+  bool PrintTrivialNodeKind = false;
 };
 
 /// RawSyntax - the strictly immutable, shared backing nodes for all syntax.

lib/Syntax/RawSyntax.cpp

@@ -57,7 +57,8 @@ void RawSyntax::print(llvm::raw_ostream &OS, SyntaxPrintOptions Opts) const {
     return;
 
   const bool PrintKind = Opts.PrintSyntaxKind && !isToken() &&
-    !isTrivialSyntaxKind(Kind);
+    (Opts.PrintTrivialNodeKind || !isTrivialSyntaxKind(Kind));
+
   if (PrintKind) {
     printSyntaxKind(Kind, OS, Opts, true);
   }

tools/swift-syntax-test/swift-syntax-test.cpp

@@ -83,6 +83,13 @@ PrintNodeKind("print-node-kind",
               llvm::cl::desc("To print syntax node kind"),
               llvm::cl::cat(Category),
               llvm::cl::init(false));
+
+static llvm::cl::opt<bool>
+PrintTrivialNodeKind("print-trivial-node-kind",
+                     llvm::cl::desc("To print trivial syntax node kind"),
+                     llvm::cl::cat(Category),
+                     llvm::cl::init(false));
+
 static llvm::cl::opt<bool>
 Visual("v",
        llvm::cl::desc("Print visually"),
@@ -227,6 +234,7 @@ int dumpParserGen(const char *MainExecutablePath,
   SyntaxPrintOptions Opts;
   Opts.PrintSyntaxKind = options::PrintNodeKind;
   Opts.Visual = options::Visual;
+  Opts.PrintTrivialNodeKind = options::PrintTrivialNodeKind;
   SF->getSyntaxRoot().print(llvm::outs(), Opts);
   return 0;
 }