Remove ANSI colors when writing to external warnings file.

[picnixz]

Fix #11617.
Fix #11574.

In addition, I needed to fix #11574 so that testing can be done properly (otherwise the file descriptor is kept opened in write mode and it is not possible to correctly read it).

@AA-Turner Can you bump the development version 7.2.3 (or 7.3) so that I can add a CHANGES entry please?

[mgeier]

Is the --keep-colors option really necessary?

I can't imagine anyone wanting those escape sequences in their warnings file.

More importantly, I think adding this option would cause confusion with the already existing --color and --no-color options.

[picnixz]

Err.. I don't really know. Like sometimes you may want to keep the colors when you print them using some weird commands. Or for filtering.

It was just to ensure that if there was someone out there doing it, then they don't need to change much (although I would recommend using tee instead then).

[picnixz]

On a second thought, I think not having that option would be the best. People that want to keep colors should simply tee the standard output I think.

Since I am away, I won't be able to update the PR soon. At least, it would simplify a bit the logic and reduce the number of CLI options for the end-user to remember.

[picnixz]

So, I removed --keep-colors since it's indeed not a good idea to keep (and it simplified the flow).

[picnixz]

I'll make the changes today or tomorrow and add a CHANGES entry as well.

[AA-Turner]

Thanks @picnixz!