ENH: Styler.background_gradient to accept vmin vmax and dtype Int64
For `vmin` `vmax` use the same implementation as `Styler.bar`
For dtype `Int64` issue, deprecated `.values` and use `.to_numpy` instead
Here explicitly assign the dtype to float since we are doing normalize

- [x] closes #12145 and #28869
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Thanks @immaxchen!