Fix Period not using freq when using same base-freq.
- [ ] closes #xxxx (Replace xxxx with the Github issue number)
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Something that threw me off:

```py
In [30]: p = pd.Period("2020-01-01", "2d")

In [31]: p.asfreq(p.freq)
Out[31]: Period('2020-01-02', '2D')
```

Since the default for `how` of `.asfreq` is `end`, this means that using `.asfreq` is not a no-op when using multiple frequencies. In other words, I find the behaviour insane and inconsistent:

```py
In [2]: import pandas as pd

In [3]: dr = pd.date_range("2020", freq="2d", periods=3)

In [4]: dr.to_series().asfreq("2d")
Out[4]: 
2020-01-01   2020-01-01
2020-01-03   2020-01-03
2020-01-05   2020-01-05
Freq: 2D, dtype: datetime64[ns]

In [5]: dr.to_period().to_series().asfreq("2d")
Out[5]: 
2020-01-02    2020-01-01
2020-01-04    2020-01-03
2020-01-06    2020-01-05
Freq: 2D, dtype: period[2D]
```

I have to say the experience using `Period` is very bad and frustrating. This pull request is stale because it has been open for thirty days with no activity. Please [update](https://pandas.pydata.org/pandas-docs/stable/development/contributing.html#updating-your-pull-request) and respond to this comment if you're still interested in working on this. Thanks for the pull request, but it appears to have gone stale. If interested in continuing, please merge in the main branch, address any review comments and/or failing tests, and we can reopen.