Support ExtensionArray in hash_pandas_object
Closes #23066
Hello @TomAugspurger! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/arrays/base.py`](https://github.com/TomAugspurger/pandas/blob/5935febecf5f25113ade5e3c40768978c9d432ee/pandas/core/arrays/base.py) !

 - There are no PEP8 issues in the file [`pandas/core/util/hashing.py`](https://github.com/TomAugspurger/pandas/blob/5935febecf5f25113ade5e3c40768978c9d432ee/pandas/core/util/hashing.py) !

 - There are no PEP8 issues in the file [`pandas/tests/extension/base/base.py`](https://github.com/TomAugspurger/pandas/blob/5935febecf5f25113ade5e3c40768978c9d432ee/pandas/tests/extension/base/base.py) !

 - There are no PEP8 issues in the file [`pandas/tests/extension/base/methods.py`](https://github.com/TomAugspurger/pandas/blob/5935febecf5f25113ade5e3c40768978c9d432ee/pandas/tests/extension/base/methods.py) !

 - There are no PEP8 issues in the file [`pandas/tests/extension/json/test_json.py`](https://github.com/TomAugspurger/pandas/blob/5935febecf5f25113ade5e3c40768978c9d432ee/pandas/tests/extension/json/test_json.py) !

 lgtm. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23082?src=pr&el=h1) Report
> Merging [#23082](https://codecov.io/gh/pandas-dev/pandas/pull/23082?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/296c251d0e2bd112d26b980f1798db14f264b664?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/23082/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23082?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23082      +/-   ##
==========================================
+ Coverage   92.19%   92.19%   +<.01%     
==========================================
  Files         169      169              
  Lines       50911    50914       +3     
==========================================
+ Hits        46939    46942       +3     
  Misses       3972     3972
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.61% <100%> (ø)` | :arrow_up: |
| #single | `42.3% <50%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23082?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/23082/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `95.89% <ø> (ø)` | :arrow_up: |
| [pandas/core/util/hashing.py](https://codecov.io/gh/pandas-dev/pandas/pull/23082/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvdXRpbC9oYXNoaW5nLnB5) | `98.4% <100%> (+0.03%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23082?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/23082?src=pr&el=footer). Last update [296c251...5935feb](https://codecov.io/gh/pandas-dev/pandas/pull/23082?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!