Create a way to scan all configured file paths
We often want to do checks on all configured file paths:
- relative paths
- runtime immutability
- sandbox immutability
We need to scan:
- type FILENAME
- HiddenServiceDir
- Log files
- *Port unix sockets
- ControlSocket
- Any options that activate a file path, but don't allow it to be configured (OnionAuth etc.)
Follow up to legacy/trac#32339 (moved) and legacy/trac#32344 (moved).