WIP: BUG: Setting DataFrame values via iloc aligns when arguments are lists

[rhshadrach]

• closes Replacing multiple columns (or just one) with iloc does not work #22046
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

This PR currently fails two tests on Windows due to int32 vs int64, but I cant' duplicate on my machine.

pandas\tests\indexing\test_indexing.py:588
test_astype_assignment

df = df_orig.copy()
df.iloc[:, 0:2] = df.iloc[:, 0:2].astype(np.int64)
expected = DataFrame(
    [[1, 2, "3", ".4", 5, 6.0, "foo"]], columns=list("ABCDEFG")
)
>       tm.assert_frame_equal(df, expected)
E       AssertionError: Attributes of DataFrame.iloc[:, 0] (column name="A") are different
E       
E       Attribute "dtype" are different
E       [left]:  int32
E       [right]: int64

Within these test, the change made causes the setting in iloc to be done here:

pandas/pandas/core/indexing.py

Lines 1722 to 1724 in c6ad13d

	for i, loc in enumerate(ilocs):
	# setting with a list, re-coerces
	isetter(loc, value[:, i].tolist())

as opposed to the usual path here:

pandas/pandas/core/indexing.py

Lines 1695 to 1705 in c6ad13d

	for loc in ilocs:
	item = item_labels[loc]
	if item in value:
	sub_indexer[info_axis] = item
	v = self._align_series(
	tuple(sub_indexer), value[item], multiindex_indexer
	)
	else:
	v = np.nan
	isetter(loc, v)

My best guess is that this is a bug in the former path that is being uncovered by this change, but I am not sure how to fix. Any suggestions or help is much appreciated.

[rhshadrach]

Needs #34217 to be addressed first. Closing to take off the queue.