HighlightVariant(ReadOnlyMemory<Char>, String?, Boolean) from the state the previous line ended in:
see Highlight(ReadOnlyMemory<Char>, String?, ref Object?). The default ignores
state.
IReadOnlyList<(string Text, IBrush? Foreground)>? HighlightVariant(ReadOnlyMemory<char> line, string? language, bool isDark, ref object? state)