[iOS26] Fix warning in iOS26

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.

Author: rcancro

Source/Layout/ASLayoutElementPrivate.h

@@ -62,9 +62,9 @@ NS_ASSUME_NONNULL_END
 // Provides extension points for elments that comply to ASLayoutElement like ASLayoutSpec to add additional
 // properties besides the default one provided in ASLayoutElementStyle
 
-static const int kMaxLayoutElementBoolExtensions = 1;
-static const int kMaxLayoutElementStateIntegerExtensions = 4;
-static const int kMaxLayoutElementStateEdgeInsetExtensions = 1;
+enum { kMaxLayoutElementBoolExtensions = 1 };
+enum { kMaxLayoutElementStateIntegerExtensions = 4 };
+enum { kMaxLayoutElementStateEdgeInsetExtensions = 1 };
 
 typedef struct ASLayoutElementStyleExtensions {
   // Values to store extensions