Add default implementations for blocks from AnimationsManager on iOS

[piaskowyk]

Summary

This PR adds default instances for uninitialized blocks in AnimationManager on iOS. It helps avoid null exceptions in two cases:

• When reloading during Layout Animations and Shared Transitions.
• When someone has installed Reanimated but doesn't import anything from it. In this situation, these blocks will not be set, but due to swizzling in Screens, there is a possibility of calling some of these blocks.

Fixes #4836
Fixes:

Test plan

1. Run Example -> open [LA] Entering and Exiting with Layout -> click toggle -> press R in console
2. Run example from v3.4.1 crash _clearAnimationConfigForTag #4836 (comment)