DEPR: Deprecate NDFrame.filter
- [ ] xref #26642
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I propose to deprecate (DataFrame|Series).filter. The method's functionality is already in the ``.loc``method, except the regex functionality, for which I've made a proposal adding regex functionality  to ``.loc`` in #27363.

@topper-123 can you rebase can you rebase again. I've rebased. As you noted, this depends on #27363.
 @topper-123 im trying to clear the PR backlog; can this be closed pending #27363? Knowing the outstanding issue is around regex capability, maybe we should just deprecate all keywords from filter for now that aren't regex? That sounds like a stepping stone to deprecating. Wouldn't it make more sense then to just deprecate this method before 1.0 is released? I don't *think* we'd want to outright deprecate without a replacement for the regex unless we instruct users to do `df[(re.search(x) for x in df.columns)]` Oh yes, I meant choose another way to select by regex at the same time, sorry.  can you merge master and will look again I've rebased.

I do think an alternative should be settled on for the regex use case and I've had two proposals that were not accepted. So I'm not sure where this is floating currently? Thanks for the PR! But I think agreement on approach here is still outstanding. If something you want to drive forward can revisit discussion in issue first