IndexedDB connections must be closed so bfcache works

[raray]

The browser's back/forward cache doesn't work when IndexedDB has an open connection. Currently, a connection is opened here and then never closed:

idb-keyval/src/index.ts

Line 13 in 6695b17

const request = indexedDB.open(dbName);

This causes Lighthouse to fail a check (https://developer.chrome.com/docs/lighthouse/performance/bf-cache/):