* [Collections] Update collections to support iPhone X
The collections use the contentInset to compute the width of the cells.
With iPhone X, the width must take into account possible inset of the side.
This patch makes sure that the collection takes into account the adjustedContentInset, which may take the safe area into consideration.
Closes#1980
* Correct respondsToSelect
* Use macro + @available instead of NSInvocation
* Fix CollectionCellsExamples and add a swift version check to the swift example.
* Make UIScrollViewContentInsetAdjustmentAlways the default
* Remove override from CollectionsSectionInsetsExample
* [Collections] Add "editing" performance example
New example to demonstrate scrolling performance when a collection
contains a large number of cells. "Editing" mode is currently very
inefficient.
* Refactoring, pulling some code into supplemental
* Making cell identifier symbol unique