BUG: flex op with DataFrame, Series and ea vs ndarray
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

<s>I have a couple ideas in mind that might make the edit in blocks here unnecessary, but want to profile them first, so will do that cleanup in a refactor following the bugfix.</s> Updated with a much cleaner implementation, it also de-special-cases one of our timedelta64 tests.
This overlaps now with https://github.com/pandas-dev/pandas/pull/34312 I could also port your test to my PR, so can you try to explain why this fix would be better? (it might be doing more now, but considering only what is required for fixing the original issue, i.e. the interval flex op test you added) > I could also port your test to my PR

please do! Only if you agree it's a good fix (I don't fully understand the rationale of the change in this PR, so I can't really judge at this time which fix is "better") > Only if you agree it's a good fix (I don't fully understand the rationale of the change in this PR, so I can't really judge at this time which fix is "better")

I agree that #34312 is a valid fix to a legitimate regression, and is well-written, minimally-invasive.  So I would have no problem with merging it on green (especially if the test is ported).  It is especially worthwhile if we don't expect this to get merged for 1.1

The advantage of the approach in this PR is that it continues operating blockwise in cases where #34312 does not.  It also gets a bunch of code out of _combine_series_frame, which will allow for streamlining in upcoming pass. OK, I added the test in the other PR, then we can continue the discussion here regardless of the regression fix. docbuild fail looks unrelated > docbuild fail looks unrelated

It's failing everywhere -> https://github.com/pandas-dev/pandas/issues/34306 green thanks @jbrockmendel 