```
This makes it easier to debug a frozen test or a test that failed. To
debug a failed test, remove the line fs::remove_all(m_path_root);.
The pull is done in three commits:
- Create a datadir for every unit test once (and only once). This
requires the SetDataDir function to go away.
- Use the common setup in the gui unit tests. Some of those tests are
testing the init sequence, so we'd have to undo some of what the testing
setup did.
- Log to the debug.log in all tests
```
Backport of core PR16252 and PR16289 (bugfix).
Depends on D5553.