This makes the `log_file` APIs behave more like the standard `log` APIs;
i.e. they inherit the state of their associated `RecordingStream`
(app_id, rec_id, timepoint, etc...).

Also inherit the application ID while we're at it.

Makes the API much nicer to use _and_ much more consistent with the
rest.

Checks:
- [x] external loader ran manually (`python loader | rerun`)
- [x] external loader via rerun (`rerun xxx.py`)
- [x] log_file with external loader (`log_file xxx.py`)
- [x] external loader ran manually (`loader | rerun`)
- [x] external loader via rerun (`rerun xxx.rs`)
- [x] log_file with external loader (`log_file xxx.rs`)

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355
- #5379
- #5361
- #5388

---------

Co-authored-by: Andreas Reich <andreas@rerun.io>

Introduces the new `DataLoaderSettings` business to C++ and update
examples accordingly (`external_data_loader` & `log_file`).

```bash
./build/debug/examples/cpp/log_file/example_log_file --recording-id this-one --entity-path-prefix a/b/c  --time sim_time=1000 --time wall_time=1709204046 --sequence sim_frame=42 rerun_cpp/tests/main.cpp | rerun -
```

![image](https://github.com/rerun-io/rerun/assets/2910679/b979a24c-29b6-473b-91b1-de3832bea436)


Checks:
- [x] external loader ran manually (`loader.exe | rerun`)
- [x] external loader via rerun (`rerun xxx.cpp`)
- [x] log_file with external loader (`log_file xxx.cpp`)

---

Part of series of PR to expose configurable `DataLoader`s to our SDKs:
- #5327 
- #5328 
- #5330
- #5337
- #5351
- #5355
- #5379
- #5361
- #5388