Separate out non-scalar tests from scalar tests; move to ?? in follow-up
The goal I have in mind is getting to the point where we can test (and measure coverage) tslibs in isolation.   That means isolating DataFrame and Series tests from everything else.

This PR doesn't change any tests and doesn't move anything across modules, just puts DataFrame and Series tests in their own classes.  Exactly what modules those belong in I haven't thought out.

If I did this right, it shouldn't have any overlap with other outstanding PRs.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=h1) Report
> Merging [#18142](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/774030cf77a2a2aaea2663c8a3bbc5470ae23c74?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18142/graphs/tree.svg?token=eZ4WkYLtcO&width=650&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18142      +/-   ##
==========================================
- Coverage   91.38%   91.36%   -0.02%     
==========================================
  Files         164      164              
  Lines       49790    49790              
==========================================
- Hits        45501    45492       -9     
- Misses       4289     4298       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.17% <ø> (ø)` | :arrow_up: |
| #single | `39.49% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18142?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/18142?src=pr&el=footer). Last update [774030c...16ccef4](https://codecov.io/gh/pandas-dev/pandas/pull/18142?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Just pushed a commit moving these tests to the appropriate modules. > you need to be very careful with this, move less at a time maybe

Hah that was kinda the idea with the original version. can you rebase > I would do this in several stages. You are moving too much. Let's do the non-controversial things first.

Sounds good. closing as scope out of hand; replaced by multiple smaller prs