2611 rename fetch data (#2689)

* Replace fetch data with preload terminology
- Deprecate `-fetchData` and `-clearFetchedData` in favor of `-preload` and `-clearPreloadedData`
- Move `-setNeedsPreload`, `-recursivelyPreload` and `-recursivelyClearPreloadedData` to ASDisplayNode+FrameworkPrivate.h
- Update internal implementation, comments and tests

* Folllow up on #2642:
- Remove -preload and -clearPreloadedData in favor of -didEnterPreloadState and -didExitPreloadState.
- -didEnterPreloadState and -didExitPreloadState call the deprecated -fetchData and -clearFetchedData methods if they are overriden.

* Missed one in a test

* Get rid of behavior change for now.

* Revert more behavior changes, fix tests.

* Don't need these anymore.

AsyncDisplayKit/ASTableView.mm

@@ -1646,18 +1646,6 @@ static NSString * const kCellReuseIdentifier = @"_ASTableViewCell";
   [super endUpdates];
 }
 
-#pragma mark - Memory Management
-
-- (void)clearContents
-{
-  [_rangeController clearContents];
-}
-
-- (void)clearFetchedData
-{
-  [_rangeController clearFetchedData];
-}
-
 #pragma mark - Helper Methods
 
 // Note: This is called every layout, and so it is very performance sensitive.