This PR updates the IDBTransaction & IDBDatabase interfaces for new-style event pages. (see the template).

On IDBTransaction: abort and error are bubbling, complete not.
On IDBDatabase: close and versionchange events.

Link to the companion bcd PR: mdn/browser-compat-data#15006

1. If the XYZ event is bubbling

• Start with the interface the event is fired at (and not bubbling too), say xxxxxxxx, and apply part 2 or 3 below, whichever is relevant.
• For each interface it is bubbling to:
  • If onXYZ exists, delete it: yarn content delete Web/API/yyyyyyy/onXYZ --redirect /en-US/docs/Web/API/xxxxxx/XYZ_event
  • N/A If not, create a redirect: yarn content add-redirect
  • If XYZ_event, delete it: yarn content delete Web/API/yyyyyyy/XYZ_event --redirect /en-US/docs/Web/API/yyyyyyy/XYZ_event
  • N/A If not, create a redirect: yarn content add-redirect
  • List the bubbling event in each interface they bubbles to.

2. When onXYZ exists and XYZ_event not, for each onXYZ

• N/A yarn content move /Web/API/xxxx/onXYZ /Web/API/xxxx/XYZ_event
• N/A Update browser-compat front-runner key
• N/A Update title front-runner key to: Interface: XYZ event (with ticks!)
• N/A Remove Property and Event Handler from the tag list and add Event instead (more cleaning possible)
• N/A Check if the event bubbles. Do nothing if not.
  • N/A Add a sentence about bubbling in the description:
  • N/A Add a Bubbling section.
• N/A Change intro to explain the event itself and no more just onXYZ.

  Example: "The levelchange event of the Battery Status API is fired when the battery {{domxref("BatteryManager.level","level")}} property is updated."

• N/A Copy the syntax section from the template, and fix the names of event and of the onXYZ property
• N/A Add the Event type section (two texts possible! If inheritance is not only Event, do these additional steps:
  • N/A Update the argument of {{InheritanceDiagram}}
  • N/A Add the Event properties section and list the parameters, taken from the interface of the event type
• N/A Check that no mention of this onXYZ is a link.
• N/A Check that links to onXYZ is a link to the adequate XYZ_event

3. When both onXYZ and XYZ_event exist:

• Move any relevant info from onXYZ to XYZ_eventpage
• Check if the event bubbles. Do nothing if not.
  • Add a sentence about bubbling in the description:
  • Add a Bubbling section.
• Update intro to explain the event itself (it may be already ok).

  Example: "The levelchange event of the Battery Status API is fired when the battery {{domxref("BatteryManager.level","level")}} property is updated."

• Copy the syntax section from the template, and fix the names of event and of the onXYZ property
• Add the Event type section (two texts possible! If inheritance is not only Event, do these additional steps:
  • N/A Update the argument of {{InheritanceDiagram}}
  • N/A Add the Event properties section and list the parameters, taken from the interface of the event type
• Check that no mention of this onXYZ is a link.
• Check that links to onXYZ is a link to the adequate XYZ_event
• yarn content delete Web/API/xxxx/onXYZ --redirect /en-US/docsWeb/API/xxxx/XYZ_event

4. On the API interface page:

• If existing, remove the Event handlers section
• If not there, add the Events section
• Check that there are no links to onXYZ.

5. On each page of the interface and the API overview page:

• Check that there are no links to onXYZ.
• Check that examples uses the modern syntax for defining function in event handler (onXYZ = event => { …} )
• Check that no {{event} macro is left.
• Fix flaws (as much as possible); at least, make sure not to introduce new flaws.
• Check that if an event is linked to a property value, that property documents when this event is fired.

  Example: "When its value changes, the chargingchange event is fired."

6. Optional:

• Remove gremlins (non-breaking spaces, curly tick, curly double-ticks)
• If the interface is no more experimental, remove the experimental tags/banners.

7. Administrative:

• Link to the BCD PR.