Ensure conversion to "native" types for integer EA
- [x] closes #29738
- [x] tests added / passed
- [x] passes `black pandas`

One test is failing. see, https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=26857&view=logs&j=bef1c175-2c1b-51ae-044a-2437c76fc339&t=770e7bb1-09f5-5ebf-b63b-578d2906aac9&l=169

I think it is because the series is being converted into int8 dtype somehow. Any thoughts? Hey @rushabh-v - sorry for only getting round to this now.

> One test is failing. see, https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=26857&view=logs&j=bef1c175-2c1b-51ae-044a-2437c76fc339&t=770e7bb1-09f5-5ebf-b63b-578d2906aac9&l=169

The build no longer exists. I'll just make another couple of suggestions, if you then ping me when you've done them I'll take a look at the failing tests Also, a whatsnew entry will be required (v1.1.0, I believe) @MarcoGorelli I have made all the changes. Can you please take a look at the logs now? see https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=28135&view=logs&j=bef1c175-2c1b-51ae-044a-2437c76fc339&t=770e7bb1-09f5-5ebf-b63b-578d2906aac9&l=125 Sure, I'll look at this later this week.

(note to self: to reproduce the error:
```
pytest pandas/tests/extension/test_integer.py
```
) I think there might be another underlying problem here, which I've raised in #31899.  So can you review and merge this PR now or we should wait for #31899 to be resolved? Yes, the tests should be passing before we can merge. I'll look into 31899 today Current tests fail because of this:
```
>>> import pandas as pd
>>> s1 = pd.Series([100], dtype='Int8')                                                                     
>>> s2 = pd.Series([100], dtype='Int8')
```
So, _without_ the current fix, we have
```
>>> [a+b for (a, b) in zip(s1.values, s2.values)]
[-56]
>>> s1.combine(s2, lambda x, y: x+y)                                                                        
0    -56
dtype: Int64
```

_With_ the current fix:
```
>>> [a+b for (a, b) in zip(s1.values, s2.values)]
[200]
>>> s1.combine(s2, lambda x, y: x+y)                                                                        
0    -56
dtype: Int64
```

cc @jorisvandenbossche  @rushabh-v is this still active? Can you merge master and try to get green? still fails Any updates? Not from me - I removed the 'good first issue' tag from the original issue as I think there's some underlying issues that need to be solved here first, and they aren't so easy @rushabh-v can you merge master closing in favor of #37377