React 19 compatibility about jetpack

[anomiex]

Something else we'll want to consider is switching to the new jsx transform if we're not already using it everywhere. Or, more specifically, whether we want to "polyfill" the react-jsx-runtime script being added to WordPress core in 6.6 for as long as we continue to support 6.5, or continue with letting the jsx runtime be included in our bundles until we drop 6.5.

[zinigor]

As far as I could find, we're not affected by either dropping the react-shallow-renderer/shallow, nor the unmountComponentNode calls. So from my understanding, the major problem is the propType, because it's abundant in Jetpack code. It's not actually breaking because it's simply going to get ignored, but still that's not a good thing.

So we should prioritize the JSX transform changes and polyfill, and the findDomNode usage.