cleanup output for gitlab writer

[baronfel]

• don't write ansi escape codes because gitlab does that now, and
• sanitize the KnownTags descriptions to prevent line overlaps

Description

After #2477 I tested the output on my work builds and got output like:

[37;2msection_start:1583446351:target_Clean
\e[0K[0m
[37;2msection_start:1583446351:target_ReplaceTemplateFilesNamespace
\e[0K[0m
[0Ksection_start:1583446308:restore_cache
[0Ksection_end:1583446309:restore_cache
[0Ksection_start:1583446309:download_artifacts
[0Ksection_end:1583446311:download_artifacts
[0Ksection_start:1583446311:build_script

Problems I see:

• newlines in the tag descriptions
• ansi escape codes from the ansi color output writer

So I corrected both of these.