Migrate MIME-type lookup to UTType (UniformTypeIdentifiers)

Replace the deprecated CoreServices UTI calls
(UTTypeCreatePreferredIdentifierForTag / UTTypeCopyPreferredTagWithClass)
in GCDWebServerGetMimeTypeForExtension with the modern
[UTType typeWithFilenameExtension:].preferredMIMEType, removing the
-Wdeprecated-declarations pragma. Behavior is unchanged: known
extensions map to the same MIME type, unknown ones fall back to the
default.

The UniformTypeIdentifiers framework (macOS 11+ / iOS 14+ / tvOS 14+,
within the project's deployment targets) is now linked in all three
build systems: Xcode (OTHER_LDFLAGS), CocoaPods (Core subspec
frameworks), and SwiftPM (linkedFramework).

Verified: Run-Tests.sh, swift build, and pod lib lint all pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GCDWebServer/Core/GCDWebServerFunctions.m

@@ -35,6 +35,7 @@
 #else
 #import <SystemConfiguration/SystemConfiguration.h>
 #endif
+#import <UniformTypeIdentifiers/UniformTypeIdentifiers.h>
 #import <CommonCrypto/CommonDigest.h>
 
 #import <ifaddrs.h>
@@ -176,17 +177,7 @@ NSString* GCDWebServerGetMimeTypeForExtension(NSString* extension, NSDictionary<
       mimeType = [builtInOverrides objectForKey:extension];
     }
     if (mimeType == nil) {
-      // These CoreServices UTI functions are deprecated since macOS 12 / iOS 15 in favor of the
-      // UniformTypeIdentifiers UTType class, but they still work and avoid pulling in a new framework
-      // dependency across the Xcode/CocoaPods/SPM builds. Silence the deprecation under -Werror.
-#pragma clang diagnostic push
-#pragma clang diagnostic ignored "-Wdeprecated-declarations"
-      CFStringRef uti = UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (__bridge CFStringRef)extension, NULL);
-      if (uti) {
-        mimeType = CFBridgingRelease(UTTypeCopyPreferredTagWithClass(uti, kUTTagClassMIMEType));
-        CFRelease(uti);
-      }
-#pragma clang diagnostic pop
+      mimeType = [UTType typeWithFilenameExtension:extension].preferredMIMEType;
     }
   }
   return mimeType ? mimeType : kGCDWebServerDefaultMimeType;