Add native file picker to core test UI

shared/src/iosMain/kotlin/com/vnidrop/app/core/FilePicker.ios.kt

@@ -0,0 +1,67 @@
+package com.vnidrop.app.core
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import kotlinx.cinterop.ExperimentalForeignApi
+import platform.Foundation.NSURL
+import platform.UIKit.UIApplication
+import platform.UIKit.UIDocumentPickerDelegateProtocol
+import platform.UIKit.UIDocumentPickerViewController
+import platform.UIKit.UIModalPresentationFormSheet
+import platform.UniformTypeIdentifiers.UTTypeItem
+import platform.darwin.NSObject
+
+private var retainedPickerDelegate: DocumentPickerDelegate? = null
+
+@Composable
+actual fun rememberShareFilePicker(
+	onFilePicked: (PickedShareFile) -> Unit,
+	onError: (String) -> Unit,
+): ShareFilePicker = remember(onFilePicked, onError) {
+	object : ShareFilePicker {
+		@OptIn(ExperimentalForeignApi::class)
+		override fun pickFile() {
+			val presenter = UIApplication.sharedApplication.keyWindow?.rootViewController
+			if (presenter == null) {
+				onError("Could not find an iOS view controller for the document picker")
+				return
+			}
+
+			val picker = UIDocumentPickerViewController(forOpeningContentTypes = listOf(UTTypeItem), asCopy = false)
+			val delegate = DocumentPickerDelegate(onFilePicked, onError)
+			retainedPickerDelegate = delegate
+			picker.delegate = delegate
+			picker.modalPresentationStyle = UIModalPresentationFormSheet
+			presenter.presentViewController(picker, animated = true, completion = null)
+		}
+	}
+}
+
+actual suspend fun sharePickedFile(
+	repository: CoreRepository,
+	file: PickedShareFile,
+	transferName: String,
+	senderName: String,
+) {
+	repository.shareSecurityScopedFileUrl(file.value, file.displayName, transferName, senderName)
+}
+
+private class DocumentPickerDelegate(
+	private val onFilePicked: (PickedShareFile) -> Unit,
+	private val onError: (String) -> Unit,
+) : NSObject(), UIDocumentPickerDelegateProtocol {
+	override fun documentPicker(controller: UIDocumentPickerViewController, didPickDocumentsAtURLs: List<*>) {
+		val url = didPickDocumentsAtURLs.firstOrNull() as? NSURL
+		if (url == null) {
+			onError("The selected iOS document URL was invalid")
+		} else {
+			val displayName = url.lastPathComponent ?: "transfer"
+			onFilePicked(PickedShareFile(url.absoluteString ?: url.path.orEmpty(), displayName))
+		}
+		retainedPickerDelegate = null
+	}
+
+	override fun documentPickerWasCancelled(controller: UIDocumentPickerViewController) {
+		retainedPickerDelegate = null
+	}
+}