[iOS26] Fix warning in iOS26

[rcancro]

When compiling in Xcode 26 we get the warning variable length array folded to constant array as an extension for the arrays in this struct:

typedef struct ASLayoutElementStyleExtensions {
  // Values to store extensions
  BOOL boolExtensions[kMaxLayoutElementBoolExtensions];
  NSInteger integerExtensions[kMaxLayoutElementStateIntegerExtensions];
  UIEdgeInsets edgeInsetsExtensions[kMaxLayoutElementStateEdgeInsetExtensions];
} ASLayoutElementStyleExtensions;

To make it happy we could make these constants #define or stick them in an enum. I chose the latter.