Continue de-nesting core.ops
- Move `isinstance(other, ABCDataFrame)` checks to consistently be the first thing checked in Series ops

- Remove `force` kwarg, define it in the one place it is used.

- Remove kludge for `PeriodIndex`

- Handle categorical_dtype earlier in arith_method_SERIES, decreasing complexity of the closure.

- Handle scalar na other earlier in _comp_method_SERIES, decreasing complexity of the closure.

- Remove broken broadcasting case from _arith_method_FRAME (closes #19421)
Just had to revert the removal of an ugly case, longstanding bug #5284, #5035. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19448?src=pr&el=h1) Report
> Merging [#19448](https://codecov.io/gh/pandas-dev/pandas/pull/19448?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/ca4ae4f1798fb63c707c6cca79e1f586cae63391?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19448/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/19448?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19448      +/-   ##
==========================================
+ Coverage   91.62%   91.62%   +<.01%     
==========================================
  Files         150      150              
  Lines       48728    48732       +4     
==========================================
+ Hits        44645    44650       +5     
+ Misses       4083     4082       -1
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.99% <100%> (ø)` | :arrow_up: |
| #single | `41.75% <48.64%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19448?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/19448/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.26% <ø> (ø)` | :arrow_up: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/19448/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `95.74% <100%> (+0.21%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19448?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/19448?src=pr&el=footer). Last update [ca4ae4f...399fcd5](https://codecov.io/gh/pandas-dev/pandas/pull/19448?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!