TST: add copy/view test for setting columns with an array/series
Similarly as https://github.com/pandas-dev/pandas/pull/46979, this is adding some test cases explicitly testing copy/view behaviour for a specific topic: if we set an array or series as a column, is the new column a copy or a view of the original data? 
At this moment, we actually already do make a copy of that data (with one exception being the cached RangeIndex values). So the tests I added here are confirming that current behaviour in tests, and adding a few checks where Copy-on-Write could delay the copy. 


32-bit test issue: https://github.com/pandas-dev/pandas/runs/6522019534?check_suite_focus=true Yes, should be fixed now! nitpicks, otherwise LGTM.  i really liked the comments @jorisvandenbossche ! Thanks @jorisvandenbossche 