Use query builder in JUpdater->findUpdates()

### Testing instructions
Make sure that Joomla updates and extensions updates are found after the patch is applied.

### Proposed Changes
- Change the `$query` to use the querybuilder.
- Use an inner join instead of a subselect
- Do a proper filter if `$eid` is passed as a single integer. Currently it is expected as an array of integers and will do no filtering at all if a single integer is passed instead of an array. Instead it will search for updates in all sites, slowing down the process. We pass a single integer in some places, like in the Joomla Update component. Thus this should be a bit faster with this patch.