4.0 | Make sure everything that was merged/included in the 3.x branch is also included in 4.0 / Rebase the branch

[jrfnl]

The 4.0 branch was branched off in January 2020 (just after the 3.5.4 release) and aside from 4.x specific changes, (nearly) all changes which have gone into the 3.x branch since then, should also be included in the branch.
Additionally, changes which have been merged up into the 4.x branch should, at times, have been updated/adjusted to comply with changed functionality in the 4.x branch.

To verify this is difficult with the branches as they currently are, especially as 4.0 has been such a long-running branch already.

I'm contemplating how to verify this properly and my current line of thinking is to rebase (and partially recreate) the 4.x branch on top of the current dev-master branch.

While I don't expect this will cause significant problems for contributors and/or external standards, it would mean that:

• Contributors who have a local 4.0 branch will need to reset that branch after the rebase.
• Contributors who have local/public branches created for the 4.0 branch, will need to rebase those branches.

I'm opening this issue to raise awareness about this intention and to allow for people to raise concerns about this plan.
If you have any (concerns), please speak up and leave a comment.

Time-line wise, I expect to execute this change some time in the new year, in two or three months time.

[jrfnl]

Related links for when this task will be executed:

• https://github.com/squizlabs/PHP_CodeSniffer/issues?q=is%3Aissue+milestone%3A4.0.0+is%3Aclosed
• https://github.com/squizlabs/PHP_CodeSniffer/pulls?q=is%3Apr+milestone%3A4.0.0+is%3Aclosed

Note: these lists won't be complete, as commits have been made straight into the 4.0 branch without PR.