Fix animation bug in 32bit when fromValue is double.

[cxfeng1-zz]

Now RCTAnimationExperimentalManager is not working on 32bit devices.

NSValue *fromValue = [view.layer.presentationLayer valueForKeyPath:keypath];
CGFloat fromFields[count];
[fromValue getValue:fromFields];

If the fromValue is kind of double value which needs two bytes in 32bit device and the count is 1, the fromFileds array will go wrong.

[brentvatne]

This sounds good to me, however AnimationExperimental is deprecated. @vjeux do we want to accept patches for this?

[vjeux]

@brentvatne doesn't hurt while there's no other solution

[brentvatne]

Should be an easy review and import for @nicklockwood