Before:
```
In [1]: np.dtype({"names": ["a"], "formats": [int], "offsets": [2]})
Out[1]: dtype({'names':['a'], 'formats':['<i8'], 'offsets':[2], 'itemsize':10})
```

After:
```
In [1]: np.dtype({"names": ["a"], "formats": [int], "offsets": [2]})
Out[1]: dtype({'names': ['a'], 'formats': ['<i8'], 'offsets': [2], 'itemsize': 10})
```

* Allow switching back to old dtype printing format.

* Add changelog.

Fixes #18609

Co-Authored-By: Eric Wieser <425260+eric-wieser@users.noreply.github.com>

It's been non-functional for the past 8 years (xref https://github.com/numpy/numpy/pull/459)