[WebAPI] IndexedDB, Fx 71 tasks

[chrisdavidmills]

Trello

https://trello.com/c/StA65qFA/113-indexeddb-api-fx-71

Acceptance criteria

1. • Implement IDBTransaction commit() method (page already exists but needs cleaning up, guides probably need to mention it, BCD needs doing)

[chrisdavidmills]

Documentation completed:

• https://wiki.developer.mozilla.org/en-US/docs/Web/API/IDBTransaction
• https://wiki.developer.mozilla.org/en-US/docs/Web/API/IDBTransaction/commit
• Compat data added: adding data for IDBTransaction.commit browser-compat-data#5118
• Rel note added: https://wiki.developer.mozilla.org/en-US/docs/Mozilla/Firefox/Releases/71#APIs