CLN: Unify signatures in _libs.groupby
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

xref https://github.com/pandas-dev/pandas/pull/33630#discussion_r428737327

The main goal is to allow _get_cythonized_result to be used with the cython implementation of var. In order to do this, it was best to modify the signatures in _libs.groupby of 

 - group_any_all;
 - _group_var; and
 - group_quantile

so that the order of the arguments matches other cython functions (e.g. those used in ops.BaseGrouper.aggregate or transform).

Note this PR has the fix for #33955 that is also in #33988 - that PR should be merged first.

Tests using %timeit on dataframes of various shapes (code for generating is at the bottom):

![image](https://user-images.githubusercontent.com/45562402/83825639-e3cf8a00-a6a7-11ea-84c7-c224870cae8b.png)

I looked into the last row. 26.7% of the time is spent in just iterating over the columns, 12.8% in the cython call, and 35.7% in the call to ``_wrap_aggregated_output``.

While working on this, it seemed best to implement ``ddof != 1`` in cython for var. The following code takes 26.5ms on master and 3.88ms in this PR.

````
ncol, order = 1, 6
df = pd.DataFrame(np.random.uniform(low=0.0, high=10.0, size=(10**order, ncol)))
df['key'] = np.random.randint(0, 50, (10**order, 1))
g = df.groupby('key')
t = %timeit -o g.std(ddof=4)
````