V4 classic as default

[mununki]

This PR makes the jsx ppx v4 + classic mode as default. The related discussion is #5505
Here are the cases of how the jsx ppx is activated.

1. Old config reason.react_jsx -> V4 + classic
2. New config -> V4 + classic or automatic as it configures
3. No config -> not activated.

[mununki]

The jsx ppx is not activated if the jsx config(old or new) doesn't exist.
Still not sure about making the v4 classic as default when the configuration about jsx doesn't exist. It will make one thing less for the new comer to learn, but the jsx ppx is always activated even if it is unnecessary.

[cristianoc]

The jsx ppx is not activated if the jsx config(old or new) doesn't exist.
Still not sure about making the v4 classic as default when the configuration about jsx doesn't exist. It will make one thing less for the new comer to learn, but the jsx ppx is always activated even if it is unnecessary.

I went back to the discussion, and there was no agreement to do this.
It seems to be one certain thing and one uncertain thing.

• certain: this is a breaking change
• uncertain: there are also advantages to do this

If you wish to go ahead with this change, better first get consensus from the forum, as that's more then 2 opinions.

[mununki]

Oh, sorry, I misunderstood. I thought we had an agreement. I'll hold this PR as a draft, but I'll ask the community about the V4 as default. It is worth asking.

[mununki]

This PR can be closed due to introducing #5661