Speed up regex comment detector pattern.

src/Workspaces/Core/Portable/EmbeddedLanguages/RegularExpressions/LanguageServices/RegexPatternDetector.cs

@@ -43,7 +43,7 @@ internal sealed class RegexPatternDetector
         /// Option names are the values from the <see cref="RegexOptions"/> enum.
         /// </summary>
         private static readonly Regex s_languageCommentDetector =
-            new Regex(@"\blang(uage)?\s*=\s*regex(p)?\b((\s*,\s*)(?<option>[a-zA-Z]+))*",
+            new Regex(@"^((//)|(')|(/\*))\s*lang(uage)?\s*=\s*regex(p)?\b((\s*,\s*)(?<option>[a-zA-Z]+))*",
                 RegexOptions.ExplicitCapture | RegexOptions.IgnoreCase | RegexOptions.Compiled);
 
         private static readonly Dictionary<string, RegexOptions> s_nameToOption =