JSX: Use <> Fragments with transforms

[sirreal]

Description

#15120 adds Fragment handling to @wordpress/babel-plugin-import-jsx-pragma and prepares @wordpress/babel-preset-default for the WordPress environment.

Leverage the <></> automatic Fragment import provided by the babel transform included in the preset. Follow-up to #15120.

How has this been tested?

Inspect transformed code to ensure imports and JSX transforms are working correctly.
Smoke test code using <></>.

Types of changes

Janitorial.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[gziolo]

I like how it simplifies the code by removing the need to import Fragment explicitly 👍

I'm wondering whether it should be enforced to use <> in Gutenberg from now on with ESLint rule?

Another question is, how we can communicate in docs that both createElement and Fragment are handled behind the scenes when you use the recommended Babel plugin. /cc @mkaz and @nosolosw

[sirreal]

I'm wondering whether it should be enforced to use <> in Gutenberg from now on with ESLint rule?

I do think this syntax should be preferred, however there are still places where <Fragment key={ key }> is necessarily used because <> does not support keys. Any rule would need to be smart enough to discern. In this PR I left files including Fragments with and without keys to use the full <Fragment> in all cases.

[aduth]

There's a merge conflict to be addressed. It otherwise appears in good order. The specific syntax is a bit off-putting to me (vs. the "explicit" Fragment), but I sense it's a matter of becoming accustomed to, and can be reinforced as a pattern increasingly common to any React project.

[gziolo]

The specific syntax is a bit off-putting to me (vs. the "explicit" Fragment), but I sense it's a matter of becoming accustomed to, and can be reinforced as a pattern increasingly common to any React project.

I share the same sentiment, in general, it should simplify everything :)