Centralize ops kwarg specification
Follow-up to #19346, making **kwargs more explicit, documenting how they are chosen, moving one method from `Panel` that belongs in `core.ops`.

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

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=h1) Report
> Merging [#19396](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d3f7d2a666aa824e2df98083aa5c1fd9bb63252e?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `95.5%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19396/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19396      +/-   ##
==========================================
+ Coverage   91.65%   91.65%   +<.01%     
==========================================
  Files         150      150              
  Lines       48726    48733       +7     
==========================================
+ Hits        44658    44667       +9     
+ Misses       4068     4066       -2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.02% <95.5%> (ø)` | :arrow_up: |
| #single | `41.76% <55.05%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/sparse/array.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL2FycmF5LnB5) | `91.48% <100%> (-0.34%)` | :arrow_down: |
| [pandas/core/panel.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcGFuZWwucHk=) | `97.3% <100%> (+0.34%)` | :arrow_up: |
| [pandas/core/sparse/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL2ZyYW1lLnB5) | `94.8% <100%> (ø)` | :arrow_up: |
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.26% <100%> (-0.04%)` | :arrow_down: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `95.52% <95.18%> (+0.22%)` | :arrow_up: |
| [pandas/core/reshape/merge.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZXJnZS5weQ==) | `94.21% <0%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `83.85% <0%> (+0.01%)` | :arrow_up: |
| [pandas/io/parquet.py](https://codecov.io/gh/pandas-dev/pandas/pull/19396/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnF1ZXQucHk=) | `72.07% <0%> (+0.51%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=footer). Last update [d3f7d2a...89692f7](https://codecov.io/gh/pandas-dev/pandas/pull/19396?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!