fix DateOffset eq to depend on normalize attr
This has a bullet point in #18854 but doesn't appear to have its own issue.

Current:
```
now = pd.Timestamp.now()
off = pd.offsets.Week(n=1, normalize=False)
normed = pd.offsets.Week(n=1, normalize=True)

>>> now + off == now + normed
False
>>> off == normed  # PR changes this comparison to False
True
```

- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
