Use built-in sheet for asset picker on iOS 15

Tusker/Screens/Compose/ComposeHostingController.swift

@@ -245,6 +245,25 @@ extension ComposeHostingController: ComposeUIStateDelegate {
     }
     
     func presentAssetPickerSheet() {
+        #if SDK_IOS_15
+        if #available(iOS 15.0, *) {
+            let picker = AssetPickerViewController()
+            picker.assetPickerDelegate = self
+            picker.modalPresentationStyle = .popover
+            picker.overrideUserInterfaceStyle = .dark
+            let sheet = picker.popoverPresentationController!.adaptiveSheetPresentationController
+            sheet.detents = [.medium(), .large()]
+            sheet.prefersEdgeAttachedInCompactHeight = true
+            self.present(picker, animated: true)
+        } else {
+            presentOldAssetPickerSheet()
+        }
+        #else
+        presentOldAssetPickerSheet()
+        #endif
+    }
+    
+    private func presentOldAssetPickerSheet() {
         let sheetContainer = AssetPickerSheetContainerViewController()
         sheetContainer.assetPicker.assetPickerDelegate = self
         self.present(sheetContainer, animated: true)