Clean lexer

[forki]

• Removed unused permitFsharpKeywords switch
• cleaned up pattern matching

[dsyme]

Please double check this return-a-tuple-and-match-on-it formulation produces code at least as good as before. I still tend to write the mutable by hand in performance-critical code but I know there is an optimization that should give us the right code here.

[forki]

  internal static Parser.token KeywordOrIdentifierToken(Lexhelp.lexargs args, LexBuffer<char> lexbuf, string s)
  {
    Parser.token token1 = (Parser.token) null;
    bool flag = Lexhelp.Keywords.keywordTable.TryGetValue(s, out token1);
    Parser.token token2 = token1;
    if (flag)
    {
         ...
    }
  }

[forki]

Somehow the build is broken (unrelated to this)

Installed:
    93 package(s) to C:\projects\visualfsharp-3dtit\lkg\project.json
Error: dotnet restore failed

#sigh

[dsyme]

Thanks for checking the generated code!

[dsyme]

@KevinRansom We can merge this once CI is fixed

[KevinRansom]

@forki Thank you for taking care of this