RichText: mark onSplit as unstable

[ellatrix]

Description

onSplit is an being revised in #11005, but it's not sure when we can land this change. In the meantime it would be good to mark onSplit as unstable. It's a relatively small deprecation. I don't expect many non core blocks to use this prop. Even in core we only use it for 3 blocks.

How has this been tested?

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[youknowriad]

I still see it in the native versions of heading and paragraph, not sure how to go about that. cc @gziolo @hypest

[ellatrix]

@youknowriad That's probably fine, RichText is entirely different there as well, handling the onSplit prop.

[youknowriad]

Ideally they should align because the goal is that plugin author using RichText will have a block working in both editors without code changes. It's probably not as urgent as 4.4 but something we should follow-up on.

[youknowriad]

I'm merging this, let's make sure we follow-up with what's needed for mobile.

[hypest]

Late to the party but, @daniloercoli , @diegoreymendez can you check if there are things we need to do or update for the gutenberg-mobile side? Thanks!

[daniloercoli]

I've created a new issue for this gutenberg-mobile side, since we want to port the changes above to mobile. Probably in the beta Milestone.