Object to tokenize a line of F# source code, starting with the given lexState. The lexState should be FSharpTokenizerLexState.Initial for the first line of text. Returns an array of ranges of the text and two enumerations categorizing the tokens and characters covered by that range, i.e. FSharpTokenColorKind and FSharpTokenCharKind. The enumerations are somewhat adhoc but useful enough to give good colorization options to the user in an IDE. A new lexState is also returned. An IDE-plugin should in general cache the lexState values for each line of the edited code.