This PR adds functionality to skip around ANSI escape sequences in catch_textflow so they do not contribute to line length and line wrapping code does not split escape sequences in the middle. I've implemented this by creating a AnsiSkippingString abstraction that has a bidirectional iterator that can skip around escape sequences while iterating. Additionally I refactored Column::const_iterator to be iterator-based rather than index-based so this abstraction is a simple drop-in for std::string.
Currently only color sequences are handled, other escape sequences are left unaffected.
Motivation: Text with ANSI color sequences gets messed up when being output by Catch2 #2833.