Fix Dataset._get_field_info() error message for unfindable field

[neutrinoceros]

PR Summary

Currently, when Dataset._get_field_info() is fed bad data (unfindable field), it raises an error which contains a seemingly random ftype value, unrelated to external input.

This fixes it

import yt
ds = yt.testing.fake_amr_ds()
ds.r["hello"]
old >> YTFieldNotFound: Could not find field '('stream', 'hello')' in AMRGridData.
new >> YTFieldNotFound: Could not find field ('unknown', 'hello') in AMRGridData.

PR Checklist

• pass flake8 yt/
• pass isort . --check --diff
• pass black --check yt/

[munkm]

Hey I'm just moving the enhancement label on this because when we do our release notes this should be categorized as a bug.

[neutrinoceros]

@FIdo test this please

[munkm]

@yt-fido test this please

[neutrinoceros]

@yt-fido test this please

[neutrinoceros]

quick note that once this is approved and merged, we should take another look at broken examples in #2723, two of which are failing with YTFieldNotFound or related errors.

[matthewturk]

This looks good to me. Some of this logic could be avoided if we did not allow for ambiguous field access.