CLN: Standardize indentation and alphabetize deps
I can't fix a problem that makes zero sense to me (#18089), but in the interests of being a team player, I can try to contribute around the periphery.

This just takes the `ext_data` dict and a) standardizes the indentation, b) arranges the entries in alphabetical order.  It is straightforward to check that the version of the dict here `==` the version in master.  The main reason to do this is so that the diff in the next step is easy to review.  

The next step is to go through and identify pyx files that don't cimport _anything_  e.g. `_libs.testing` and fill out their `ext_data` entries with the appropriate `[]`s (note that the processing of `ext_data` inserts default values for missing keys, so adding `[]` entries _is_ part of the specification).

There are a few modules that meet that description, then a handful of others that only have cimports from numpy (e.g. io.sas._sas).  Those entries can be fully filled out independently of any other outstanding issues.
this is fine (assume it lints ok)
ping on green as far as the other issue
i would simply add pxd as appropriate # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=h1) Report
> Merging [#18104](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5f113539d5d1bf71c9864fd382c1ab6cf5136973?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/18104/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18104      +/-   ##
==========================================
- Coverage   91.27%   91.26%   -0.02%     
==========================================
  Files         163      163              
  Lines       50123    50123              
==========================================
- Hits        45752    45744       -8     
- Misses       4371     4379       +8
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.07% <ø> (ø)` | :arrow_up: |
| #single | `40.32% <ø> (-0.06%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.75% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.5% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18104?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/18104?src=pr&el=footer). Last update [5f11353...fa71d62](https://codecov.io/gh/pandas-dev/pandas/pull/18104?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 > as far as the other issue
> i would simply add pxd as appropriate

You're gonna have to be more specific.  Or for the sake of morale, let me ignore this comment and move on with my day. @jreback : IMO we should just make sure that we get a deps list that works first and foremost.  We can cut it down afterwards.  I think that's why @jbrockmendel has been confused by what to do there.