VIS: let PeriodConverter handle datetime64 data
xref https://github.com/pandas-dev/pandas/issues/9053 (but doesn't solve it)
can you rebase / update # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18468?src=pr&el=h1) Report
> Merging [#18468](https://codecov.io/gh/pandas-dev/pandas/pull/18468?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/6ba65ca8a69560d526762bdbded64b3139f66d7a?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18468/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/18468?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18468      +/-   ##
==========================================
- Coverage   91.57%   91.56%   -0.01%     
==========================================
  Files         150      150              
  Lines       48700    48702       +2     
==========================================
  Hits        44595    44595              
- Misses       4105     4107       +2
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.93% <ø> (-0.01%)` | :arrow_down: |
| #single | `41.71% <ø> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18468?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/18468/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `66.95% <ø> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/18468/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `84.24% <0%> (-0.22%)` | :arrow_down: |
| [pandas/core/nanops.py](https://codecov.io/gh/pandas-dev/pandas/pull/18468/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvbmFub3BzLnB5) | `96.69% <0%> (+0.01%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18468?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/18468?src=pr&el=footer). Last update [6ba65ca...f20f999](https://codecov.io/gh/pandas-dev/pandas/pull/18468?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. pls add a whatsnew if you think appropriate (or not ok too).