REF: make PeriodIndex.get_value wrap PeriodIndex.get_loc
AFAICT the only behavior this changes is in how datetime objects are treated.  After this they are more consistent.

```
dti = pd.date_range("2016-01-01", periods=3, freq="MS")
pi = dti.to_period("H")
ser = pd.Series(range(7, 10), index=pi)

key = dti[0]
```

master
```
>>> pi.get_loc(key)
0
>>> pi.get_value(ser, key)
KeyError: Timestamp('2016-01-01 00:00:00', freq='MS')
>>> ser.loc[key]
7
>>> ser[key]
KeyError: Timestamp('2016-01-01 00:00:00', freq='MS')
```

Under this PR, the get_value and `__getitem__` calls both return 7.
sgtm. @jreback gentle ping, plenty more steps to go yep thanks @Meeseeksdev backport to 1.0.x

Backporting this, in an attempt to close https://github.com/pandas-dev/pandas/issues/32108. Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

```
$ git checkout 1.0.x
$ git pull
```

2. Cherry pick the first parent branch of the this PR on top of the older branch:
```
$ git cherry-pick -m1 5402ea57a6f0fe606a3de3731dcb903186b1f4c2
```

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

```
$ git commit -am 'Backport PR #31318: REF: make PeriodIndex.get_value wrap PeriodIndex.get_loc'
```

4. Push to a named branch :

```
git push YOURFORK 1.0.x:auto-backport-of-pr-31318-on-1.0.x
```

5. Create a PR against branch 1.0.x, I would have named this PR:

> "Backport PR #31318 on branch 1.0.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to [suggest an improvement](https://github.com/MeeseeksBox/MeeseeksDev).
                 Seems like backporting this will depend on too many other changes (at least PeriodIndex._get_values_for_loc). I won't pursue this any further.