IDB: SQLite store - implement index creation and cursors

createIndex() and cursors (both key-only and with value) work.
count() is implemented but needs triggers to function correctly.
Triggers are needed also to remove "tombstones", i.e., the outdated
index entries from when an object store record has been updated.

Bug: 419203258
Change-Id: I989ecb13327e74b3e44dfc6d464af510d625ecb5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6657621
Reviewed-by: Evan Stade <[email protected]>
Commit-Queue: Abhishek Shanthkumar <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1477242}

Author: abhishek-shanthkumar

IndexedDB/idbindex_tombstones.any.js

@@ -46,6 +46,15 @@ async function run_test(testCase, transactionMode, direction) {
       IDBKeyRange.bound(-11, 11), direction);
   let results = await iterateAndReturnAllCursorResult(testCase, cursor);
   assert_equals(results.length, 3);
+  // Verify count().
+  await new Promise((resolve, reject) => {
+    const countRequest = txn.objectStore('objectStore').index('index').count();
+    countRequest.onsuccess = testCase.step_func(event => {
+      assert_equals(event.target.result, 3);
+      resolve();
+    });
+    countRequest.onerror = reject;
+  });
   db.close();
 }