ways with more than 2000 nodes: prevent lockup and provide validator-fix

[tyrasd]

closes #7381:

1. prevents the locked-up state after the API returns a HTTP 400 status code after uploading a way with too many nodes
2. adds a validator which checks for such objects
3. the validator provides an easy fix by splitting the affected object into small enough pieces:

Maybe the exact wording could still be improved?