BUG: DatetimeIndex.get_loc/get_value raise InvalidIndexError
almost done with the get_value/get_loc methods
needs a rebase. not user facing right? > not user facing right?

technically get_loc is part of the Index api ok, though I feel this needs more tests, but maybe just being paranoid > ok, though I feel this needs more tests

yah, i spent most of yesterday trying to organize/flesh-out the index/indexing tests and it turned in to a yak-shaving kind of day.  this is gonna be a marathon.  xref #31241 #31193. 