fix(iOS): add missing iOS API availbility checks (#1860)

## Description

When adding 

#1843

I've forgotten to add API avaibility checks for method definitions
(usage and declarations were guarded). This caused build problems when
deploying for lower iOS versions.

Fixes #1859

## Changes

Added missing availbility checks.

## Test code and steps to reproduce

Build iOS without having iOS 16 installed (or somehow disabled?).

## Checklist

- [x] Ensured that CI passes

ios/RNSSearchBar.h

@@ -21,8 +21,11 @@
 @property (nonatomic) RNSSearchBarPlacement placement;
 @property (nonatomic, retain) UISearchController *controller;
 
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_16_0) && \
+    __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_16_0 && !TARGET_OS_TV
 - (UINavigationItemSearchBarPlacement)placementAsUINavigationItemSearchBarPlacement API_AVAILABLE(ios(16.0))
     API_UNAVAILABLE(tvos, watchos);
+#endif // Check for iOS >= 16 && !TARGET_OS_TV
 
 #ifdef RCT_NEW_ARCH_ENABLED
 #else

ios/RNSSearchBar.mm

@@ -213,7 +213,10 @@ - (void)showCancelButton
 #endif
 }
 
-- (UINavigationItemSearchBarPlacement)placementAsUINavigationItemSearchBarPlacement
+#if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_16_0) && \
+    __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_16_0 && !TARGET_OS_TV
+- (UINavigationItemSearchBarPlacement)placementAsUINavigationItemSearchBarPlacement API_AVAILABLE(ios(16.0))
+    API_UNAVAILABLE(tvos, watchos)
 {
   switch (_placement) {
     case RNSSearchBarPlacementStacked:
@@ -224,6 +227,7 @@ - (UINavigationItemSearchBarPlacement)placementAsUINavigationItemSearchBarPlacem
       return UINavigationItemSearchBarPlacementInline;
   }
 }
+#endif // Check for iOS >= 16 && !TARGET_OS_TV
 
 #pragma mark delegate methods