Implement Series.__rdivmod__, un-xfail tests

[jbrockmendel]

• closes Series has no __rdivmod__ #19252
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[jreback]

do we need to add anything to extension tests to exercise this? I think we are just testing divmod atm

    def test_divmod_series_array(self, data):
        s = pd.Series(data)
        self._check_divmod_op(s, divmod, data)

in pandas/tests/extension/base/ops.py

[jbrockmendel]

do we need to add anything to extension tests to exercise this?

I'm not very familiar with that test directory. I expect that will change after the current crop of PRs is done and I get started on Datetime/TimedeltaArray.

After Datetime/Timedelta/PeriodArray are all in place, I'm planning to add them to something like the box fixture used in tests/arithmetic. IntNA should be added there, too.

[jreback]

ok, let me create an issue for this then.