Merge v19 -> v20

[fballiano]

Cherry picking from v19.4.20...1.9.4.x

[fballiano]

#2744 had conflicts

[fballiano]

I've synced everything, notes:

• phpstan: remove one diff between v19/20 baseline #2855 seems doesn't have anything to merge
• we still have to merge Sync v19 v20 #2810 but I'd do it separately
• we should merge this, it is already too huge to handle

[sreichel]

Sync v20 can be move to next release imho.

[sreichel]

CI / Check files / Changed (pull_request)

Think we can ignore it for this release.

Problems:

• workflows should run when files are deleted, but ...
• we deleted lib/Zend at the same time ...

... output seems to be to large.

Dont know if it is worth to raise an issue at https://github.com/tj-actions/changed-files

[fballiano]

updated this today, still misses #2810 that will be handled separately.

please review and let's merge it, it's already too huge.

[fballiano]

Note: I directly pushed these two

to 20.0 because there were no conflicts

[fballiano]

pushed these directly to v20 since there were no conflicts

[fballiano]

just pushed all the new merged PRs on "20.0" branch

[luigifab]

I think there is something wrong on branch 20 for Mage.php: setIsDownloader is back, getOpenMageVersion return 19, @http_response_code(500); is removed.
Not sure if other files have problems or not.

[addison74]

@luigifab is right. Method setIsDownloader was removed here b1098b2 but if you check the code in OM 20 is still there.

[fballiano]

@luigifab the getOpenMageVersion bug is coming from #2839, it should be fixed already on branch 20.0, I've committed the right number for that method to return.

I'm checking the downloader thing now.

[fballiano]

So, setIsDownloader was coming from that same PR, this is the commit 7c5b68e

The PR was correctly forward ported (it should have been) but we should have modified the v20 version, which we didn't.

I now have removed the setIsDownloader which seems to me the only thing we should have done in v20 with PR #2839.