I prefer not create a big diff in the vcs history since we already did one. Reproducing this diff requires additional tooling which I don't like. Most of these add a trailing comma in arrays which isn't super important. I am unsure about the indentation changes in heredocs and in array key => val alignment.

I prefer not create a big diff in the vcs history since we already did one.

That’s why I proposed doing it as a part of #2872. Now we have no other choice than making a second PR.

Reproducing this diff requires additional tooling which I don't like.

You can just install it one time and then drop it with git clean. Or you can review the changes manually like I did. The alternative is leaving the formatting broken, which makes it easier for mistakes to happen.

Or we could replace CodeSniffer with PHP-CS-Fixer project-wide since it seems to work more reliably.

I felt that the PHP-CS-Fixer defaults were reasonable but can adjust the formatting further if necessary:

• Trailing array commas make refactoring easier – you can just add/remove/reorder array items without changing different lines.
• Sane heredoc syntax was introduced in PHP 7.3. It makes the code structure easier to understand since the heredocs no longer break the nesting hierarchy.
• The spacing around binary operators can be adjusted with ['operators' => ['=>' => 'align_single_space']] – but single space on both sides like any other binary operator makes more sense to me since aligning it manually is pain, both initially and every time a longer key is added.