4.3.1 changelog

[kLabz]

See https://github.com/HaxeFoundation/haxe/commits/4.3_bugfix

I put pretty much everything in there, maybe some are not worth mentioning?
Also not sure about the "breaking change"; it won't break code but will break pretty errors config and that's unexpected in a patch release so I thought it should be highlighted.

As for the date, I suppose it depends on what else we want to include + making sure packaging will be ok. Can be updated when actually preparing the release.

Would also be nice to have those around the same time or before:

• Replace travis with github actions api.haxe.org#20
• Update for 4.3 HaxeManual#526

[Simn]

Wouldn't it be better to merge this into development and then into the bugfix branch afterwards?

[kLabz]

I can cherry pick one way or another, doesn't matter much

[kLabz]

Will do it locally.