Fabric: RCTSurfaceRegistry now stores Surfaces as weak references

Summary:
@public
RCTSurfaceRegistry always promised this in the documentation but never actually did.

Reviewed By: sahrens

Differential Revision: D9652732

fbshipit-source-id: f3d06b95192e024273dc0e3a1c2753ca92370338

React/Fabric/RCTSurfaceRegistry.mm

@@ -20,7 +20,7 @@
 {
   if (self = [super init]) {
     _registry = [NSMapTable mapTableWithKeyOptions:NSPointerFunctionsIntegerPersonality | NSPointerFunctionsOpaqueMemory
-                                      valueOptions:NSPointerFunctionsObjectPersonality];
+                                      valueOptions:NSPointerFunctionsObjectPersonality | NSPointerFunctionsWeakMemory];
   }
 
   return self;