BUG: Cast ExtensionArray to numpy ndarray before plot
Cast `ExtensionArray`(eg. `IntegerArray`) to `np.ndarray` before send to matplotlib to plot, fixes #25587.

- [x] closes #25587
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry
