Clarifying another Regexp namespace

Right now there is both a v8::internal::RegExp class and a
v8::RegExp class so when code says just "RegExp" the name lookup
depends on what the compiler knows. In some jumbo builds the
compiler suddenly knew about v8::internal::RegExp which made
the symbol lookup choose that class instead of v8::RegExp.

Bug: v8:9359
Change-Id: Ic226d187a397ef2ed4e1e7b415c4f68ba72aa0e6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1669688
Auto-Submit: Daniel Bratell <bratell@opera.com>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62305}

src/parsing/parser-base.h

@@ -1595,7 +1595,7 @@ typename ParserBase<Impl>::ExpressionT ParserBase<Impl>::ParseRegExpLiteral() {
   }
 
   IdentifierT js_pattern = impl()->GetNextSymbol();
-  Maybe<RegExp::Flags> flags = scanner()->ScanRegExpFlags();
+  Maybe<v8::RegExp::Flags> flags = scanner()->ScanRegExpFlags();
   if (flags.IsNothing()) {
     Next();
     ReportMessage(MessageTemplate::kMalformedRegExpFlags);