Compile static test filler comments in the fixture output

[marioevz]

          Instead of discarding these, they should be added to `_info`'s `description` field. Could be a bit messy, as they could have come from any location in the YAML? We can create a follow-up issue?

Originally posted by @danceratopz in #1336 (comment)

[winsvega]

The comments live in Fillers only as those files are the source.

Only one comment from _info.comment is copied if its defined in Filler.

We don't need to work this out the whole thing is temporary and there are not so many comments.

Also comments will loose their descriptive power if you move it from its place and batch into info.