UpgradeVersion should return the upgraded version for IndexedDB

[rasviitanen]

When handeling the SyncOperation::UpgradeVersion case in handle_sync_operation, we currently upgrade the database version by assigning db.version = version;. As of now, this never fails and it is ok to return the value immediately. However, the database upgrade should not behave like this in once we allow multiple database connections. Instead of returning the version immediately, we should get the version from the database environment.

To illustrate:
open with version v10 -> open with version v9 -> db upgrades to v10 -> db upgrades to v9
This would result in the wrong version being returned (v9) by the upgrade version function, but the true version is v10 (we cannot downgrade the version).

Task

• Fix the upgrade logic so that the database only upgrades if the requested version is higher
• Return the version of the database environment

Files
components\net\indexeddb\idb_thread.rs