[NFC] Include implicit-unwrap bit in AST dump

There’s a bit in the AST indicating whether a ForceValueExpr is an implicitly-inserted unwrap of an IUO, but it’s not included in the AST dump. Add it.

Author: beccadax

lib/AST/ASTDumper.cpp

@@ -2659,7 +2659,11 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
   void visitForceValueExpr(ForceValueExpr *E) {
-    printCommon(E, "force_value_expr") << '\n';
+    printCommon(E, "force_value_expr");
+    if (E->isForceOfImplicitlyUnwrappedOptional())
+      PrintWithColorRAII(OS, ExprModifierColor) << " implicit_iuo_unwrap";
+    OS << '\n';
+
     printRec(E->getSubExpr());
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }