Part of #14578.

Per the new guideline: https://github.com/mdn/browser-compat-data/blob/main/docs/data-guidelines.md#dom-events-eventname_event

4 events: chargingchange_event, chargingtimechange_event, dischargingtimechange_event and levelchange_event.

Only cases where onXYZ exists, but not XYZ_event.

Move onXYZ to non-existingXYZ_event:

• Rename onXYZ to XYZ_event
• Change mdn_url to new MDN page
• Add description before mdn_url: "description": "<code>XYZ</code> event",
• Add second entry to spec_url
• Run npm run fix to fix sort (if needed)
• Run npm testto check all is fine
• Open PR with name of events.
• Add link to related content PR
• Add "needs content update" label if content PR has not been merged.
• Update description of Update event features according new data guideline #14578 so that it points to this PR

Content work: mdn/content#13021