feat: Don't scale down huge non-JPEGs, recode them first (#7977)

[iequidoo]

If after recoding to JPEG an image isn't huge anymore, don't scale it down, this preserves quality of most screenshots. For JPEGs however we don't try to recode them w/o scaling down:

• They are already JPEG-encoded, maybe with higher quality, but anyway.
• We don't want extra CPU work for most photos.

Close #7977

[j-g00da]

This whole logic chain
a && (b || c) || d && (e || f && g)
is extremely hard to read, while at it we should take few minutes to rewrite it, create some additional variables that makes it easier to comprehend. It will save us a lot of time reviewing changes around it later on.

[iequidoo]

I've simplified the logic, maybe this is enough? Moreover, there was an already existing bug that i didn't notice before probably: a non-JPEG image mayn't have exceeds_max_bytes but after removing Exif it may become huge if it can't be encoded to JPEG effectively. Now such images are downscaled.

EDIT: Well, simplified too much: made a bug that a small JPEG may be downscaled after removing Exif if it becomes "large" for some reason, e.g. if we use a less effective encoder. We don't want to recode JPEGs twice in any case. This is a corner case, but is now fixed.

[72374]

Is this PR supposed to be about improving the quality of screenshots specifically, or improving the quality of sent images in general?

[iequidoo]

Is this PR supposed to be about improving the quality of screenshots specifically, or improving the quality of sent images in general?

In general for non-JPEGs and, as a consequence, PNG screenshots. We'd like to have less format-specific code, so let's not add more PNG-specific code even if we already have some.

Otherwise the next bug would be "i sent a BMP image and it was scaled down instead of just being recoded".