- cleanup duplicate code now that #2445 is fixed
- update unit tests using old `ModelBindingContext` setups
- fix (just) one integration test where `MutableObjectModelBinder` incorrectly calculated
`isTopLevelObject` and returned a non-`null` model
- undo temporary changes in `BodyModelBinderTests` due to increased reliance on incorrect
`isTopLevelObject` in #2445 fix
nits:
- combine tests that are now duplicates
- beef up coverage of some `MutableObjectModelBinderTest` cases
- remove unused `using`s
This change treats 'top-level' collection-type models similarly to
top-level POCO model - namely that they will always be instantiated even
if there's no data to put inside.
Doug Bunting
Ryan Nowak
N. Taylor Mullen