Filters out ANSI code from string

NOTE(olafur): this is a hot execution path so the code is not implemented in the most readable or maintainable way for performance reasons. We are streaming the output from build logs to the LSP client, with basic processing like stripping out ANSI escape code that won't render nicely in the editor UI. We could write the same logic with fewer lines of code and a more readable implementation by doing something like: - convert bytes into a string - strip out ansi escape codes from string using fansi - use linesIterator to walk lines Instead, we process the chars directly to filter out unwanted ANSI escape code