Require React 18

[alexeyr-ci]

Summary

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Pull Request checklist

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• [x] Add/update test to cover these changes
• [x] Update documentation
• [x] Update CHANGELOG file
  Add the CHANGELOG entry at the top of the file.

Other Information

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[justin808]

@alexeyr-ci2 What's the point of this PR?

[alexeyr-ci2]

@justin808 Added summary.

[justin808]

How big is this;

• Optimize bundle size

Is this really worth changing now?

[alexeyr-ci2]

@justin808 It's mostly about making our code simpler, and simplifying maintenance for the future. Obviously not right now while HiChee isn't on React 18 yet. It will be more convenient to measure bundle size change once Popmenu is on ROR 15.

[justin808]

Closing stale draft PR (opened March 2025, 8 months old).

This work has been superseded by React 19 support which was recently merged:

• #1942 - React 19 webpack configuration
• #1943 - React 19 Pro package updates
• #1944 - React 19 OSS package updates

React on Rails now supports React 19, making this React 18 requirement PR obsolete.

If there are specific changes from this PR that are still relevant, please open a new PR based on current master.