[parser] Fix the MSVC build

MSVC seems to instantiate the Parser::PreParserIdentifierToAstRawString
method despite it being unused. This CL adds an (unreachable)
definition for it.

Bug: v8:12266
Change-Id: I355ca82a9d6b7bc8cd16768a8df93e40f8bfc638
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3199856Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77313}

src/parsing/parser.h

@@ -709,6 +709,13 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
     return arg;
   }
 
+  const AstRawString* PreParserIdentifierToAstRawString(
+      const PreParserIdentifier& arg) {
+    // This method definition is only needed due to an MSVC oddity that
+    // instantiates the method despite it being unused. See crbug.com/v8/12266 .
+    UNREACHABLE();
+  }
+
   IterationStatement* AsIterationStatement(BreakableStatement* s) {
     return s->AsIterationStatement();
   }