move DatetimeBlock and DatetimeTZBlock adjacent to DatetimeLikeBlockMixin
Pure cut/paste.
Hello @jbrockmendel! Thanks for submitting the PR.

 - In the file [`pandas/core/internals.py`](https://github.com/pandas-dev/pandas/blob/2d7e3d43e58b23ef50dc72505f19c4d13258343e/pandas/core/internals.py), following are the PEP8 issues :

> [Line 2459:13](https://github.com/pandas-dev/pandas/blob/2d7e3d43e58b23ef50dc72505f19c4d13258343e/pandas/core/internals.py#L2459): [E722](https://duckduckgo.com/?q=pep8%20E722) do not use bare except'

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19221?src=pr&el=h1) Report
> Merging [#19221](https://codecov.io/gh/pandas-dev/pandas/pull/19221?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8347ff8c9d8876fa46f73dbc48919a672caef1d2?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `92.54%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19221/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19221?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19221      +/-   ##
==========================================
+ Coverage   91.53%   91.55%   +0.02%     
==========================================
  Files         147      147              
  Lines       48797    48797              
==========================================
+ Hits        44664    44676      +12     
+ Misses       4133     4121      -12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.92% <92.54%> (+0.02%)` | :arrow_up: |
| #single | `41.6% <50.89%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19221?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/19221/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `94.49% <92.54%> (ø)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19221/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.95% <0%> (+1.73%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19221?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/19221?src=pr&el=footer). Last update [8347ff8...2d7e3d4](https://codecov.io/gh/pandas-dev/pandas/pull/19221?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 I agree this is ideally a better order of the classes in the file, but given that it makes blaming harder and there is currently intensive work on this file, not sure it is worth doing such a simple cut and paste (personally I often use the navigation or search of my ide anyway to navigate to a specific class) Fair enough.  Higher priorities, closing.