IDB: SQLite - implement a fast path for cursor advance

The IndexedDB spec specifies cursor position as the key of the
previously returned record and not as an index because the list of
records in the range of the cursor can change during the lifetime of the
cursor (through interleaved write operations).

To account for this, the SQLite cursor implementation reset and
re-executed the cursor query every time Continue() or Advance() was
called. Continue(), when called with a target key, needs the query to be
reset, but in the other cases, including Advance(), the cursor can get
away with Step()ing the query if it knows that no record changed in the
range since the query was last executed.

This CL adds hooks to invalidate the long-lived cursor statements at
appropriate points and updates the cursor to step the statement if it
was not invalidated. The points are: 1. Object store put 2. Object store
delete (range) 3. Clear object store 4. Prefetch reset 5. Reaching the
end of the range (if this happens during a prefetch, a subsequent call
to Advance() can be made by the renderer, which should return false).

Though the prefetch cache maintained by blink is also invalidated in the
above cases (and more; see crbug.com/442489276 ), it calls up to the
browser side via `PrefetchReset()` only if there were prefetched
records, which is not always the case. Hence, we need our own
invalidation at the DatabaseConnection level.

With this change, the abstraction provided by RecordIterator does not
seem to add much value. Hence, it has been refactored away and the
implementations in DatabaseConnection derive directly from
BackingStoreCursorImpl.

This CL results in a 17% improvement in the mail-client-read blink perf
test (reduced from 81 ms to 67 ms). The getAll() operations get a bigger
performance boost of ~50%, but on an already small baseline
(IDBObjectStore::getAll reduced from 4.8 ms to 2.9 ms, for instance).

Bug: 436880910
Change-Id: Iafb6a92071e73a21ffb2505bda813756b455bec1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6905862
Reviewed-by: Evan Stade <evanstade@microsoft.com>
Commit-Queue: Abhishek Shanthkumar <abhishek.shanthkumar@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1512977}