Fix public compilation by making METAUIKitBridge conditional

Summary:
`IGListKit` was failing to compile in public/open source builds (SPM, CocoaPods) because it unconditionally imported an internal library `METAUIKitBridge` on macOS.

The issue:
- The header `#import <METAUIKitBridge/METAUIKitBridge.h>` would fail to resolve

The fix:
- Use `__has_include` to conditionally import METAUIKitBridge only when available
- Fall back to plain `Cocoa/Cocoa.h` for public builds

This preserves internal macOS functionality while allowing the open source version of `IGListKit` to compile without the Meta-internal dependency.

Differential Revision: D101185193

fbshipit-source-id: 40cd9d9ce1bc5ad7e78cf190ced111e179e3badb

CHANGELOG.md

@@ -7,6 +7,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 ### Fixes
 
+- Fixed public compilation failure on macOS (SPM, CocoaPods) by conditionally importing METAUIKitBridge only when available. [Cameron Roth](https://github.com/camroth)
+
 - An infinite recursion crash when VoiceOver is enabled and `scrollViewDelegate` or `collectionViewDelegate` is set to the adapter's own `UICollectionView`. [Cameron Roth](https://github.com/camroth) [(#1658)](https://github.com/Instagram/IGListKit/issues/1658)
 
 5.2.0

Source/IGListDiffKit/IGListCompatibility.h

@@ -9,8 +9,10 @@
 
 #if TARGET_OS_EMBEDDED || TARGET_OS_SIMULATOR || TARGET_OS_MACCATALYST
 #import <UIKit/UIKit.h>
-#elif TARGET_OS_OSX
+#else // TARGET_OS_OSX
+#if __has_include(<METAUIKitBridge/METAUIKitBridge.h>)
 #import <METAUIKitBridge/METAUIKitBridge.h>
 #else
 #import <Cocoa/Cocoa.h>
 #endif
+#endif