static _gatherPreflightCommentStrings(model, startLineNumber, endLineNumber, languageConfigurationService) {
        model.tokenization.tokenizeIfCheap(startLineNumber);
        const languageId = model.getLanguageIdAtPosition(startLineNumber, 1);
        const config = languageConfigurationService.getLanguageConfiguration(languageId).comments;
        const commentStr = (config ? config.lineCommentToken : null);
        if (!commentStr) {
            // Mode does not support line comments
            return null;
        }
        const lines = [];
        for (let i = 0, lineCount = endLineNumber - startLineNumber + 1; i < lineCount; i++) {
            lines[i] = {
                ignore: false,
                commentStr: commentStr,
                commentStrOffset: 0,
                commentStrLength: commentStr.length
            };
        }
        return lines;
    }
Do an initial pass over the lines and gather info about the line comment string.
Returns null if any of the lines doesn't support a line comment string.