[visionOS] Add support for Firebase Performance on visionOS (#11950)

Author: andrewheard

FirebasePerformance/Sources/Instrumentation/UIKit/FPRUIViewControllerInstrument.m

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#import <TargetConditionals.h>
 #import <UIKit/UIKit.h>
 
 #import "FirebasePerformance/Sources/AppActivity/FPRScreenTraceTracker+Private.h"
@@ -68,9 +69,12 @@ void InstrumentViewDidAppear(FPRUIViewControllerInstrument *instrument,
 
     // This has to be called on the main thread and so it's done here instead of in
     // FPRScreenTraceTracker.
+    // TODO: Replace keyWindow usage (deprecated in iOS and unavailable in visionOS).
+#if !defined(TARGET_OS_VISION) || !TARGET_OS_VISION
     if ([((UIViewController *)_self).view isDescendantOfView:FPRSharedApplication().keyWindow]) {
       [[FPRScreenTraceTracker sharedInstance] viewControllerDidAppear:_self];
     }
+#endif
   }];
 }
 

Package.swift

@@ -897,7 +897,7 @@ let package = Package(
     .target(
       name: "FirebasePerformanceTarget",
       dependencies: [.target(name: "FirebasePerformance",
-                             condition: .when(platforms: [.iOS, .tvOS]))],
+                             condition: .when(platforms: [.iOS, .tvOS, .firebaseVisionOS]))],
       path: "SwiftPM-PlatformExclude/FirebasePerformanceWrap"
     ),
     .target(