schedulers/balance_region: could we merge all logic to filter region into one region filter?

## Enhancement Task
We have already use some region filter to check whether the region meet the conditions to transfer any peer, how ever, it seems we miss to create region filter for the following check:
[https://github.com/tikv/pd/blob/99e38eb7b4454cc283c0fea99518753a196b9b50/server/schedulers/balance_region.go#L198-L208](https://github.com/tikv/pd/blob/99e38eb7b4454cc283c0fea99518753a196b9b50/server/schedulers/balance_region.go#L198-L208)

So could we merge all logic to filter region into one region filter when we try to find a region to transfer peer?