This test currently only test `limit_area`.

For `limit_direction` the implementation should later raise an error,
because `pad` and `bfill` both already define a direction. But let's
now first do the implementation of the `limit_area` for `pad`
and `bfill`.

Since methods `pad` and `bfill` in `blocks.interpolate` end up
using `missing.interpolate_2d` which can not (easily) be extended
to support `limit_area`, I introduce the new function
`missing.interpolate_1d_fill`. It is a modified copy of `interpolate_2d`
but only works for 1d data and uses newly introduced function
`_derive_indices_of_nans_to_preserve`, which is now also used in
`missing.interpolate_1d`. It works the same way as the
1D-interpolation functions which are based on scipy-interpolation which
are applied via np.apply_along_axis.

…values` also was changed via appliying `func`

…e used

Test for all forbidden combos of `pad` and `backfill` is included

…d `limit_direction`

* black formatting
* typo

…ments

Test on my local machine are not affected by removing the unncessery
arguments `valid` and `invalid`, which are now derived within the
function.

…erpolate_2d`

-black formating
-remove variables that are now obsolete

…imit_area_and_limit_direction_with_pad

Manually resolved conflicts:
 * doc/source/whatsnew/v1.1.0.rst: Just a conflicting line
 * pandas/tests/series/test_missing.py: All test for interpolation have
   been moved to a new file pandas/tests/series/methods/test_interpolate.py
   I accepted all changes from upstream, which removed my tests from
   test_missing.py and manually added my test to the new file
   methods/test_interpolate.py

Co-Authored-By: William Ayd <william.ayd@icloud.com>

…imit_area_and_limit_direction_with_pad

I removed most of the code that I have added in this branch and will add it back in step by step in the next commits

Tests should be red now

provided by pandas-dev#34749

Test are green now

… into interpolate_2d

…26796-interpolate-kwargs

…26796-interpolate-kwargs

…26796-interpolate-kwargs

…26796-interpolate-kwargs