examples : add whisper.swiftui demo app (#308)

* Add SwiftUI demo project.

* Add -DGGML_USE_ACCELERATE

examples/whisper.swiftui/whisper.swiftui.demo/Utils/Recorder.swift

@@ -0,0 +1,35 @@
+import Foundation
+import AVFoundation
+
+actor Recorder {
+    private var recorder: AVAudioRecorder?
+    
+    enum RecorderError: Error {
+        case couldNotStartRecording
+    }
+    
+    func startRecording(toOutputFile url: URL, delegate: AVAudioRecorderDelegate?) throws {
+        let recordSettings: [String : Any] = [
+            AVFormatIDKey: Int(kAudioFormatLinearPCM),
+            AVSampleRateKey: 16000.0,
+            AVNumberOfChannelsKey: 1,
+            AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue
+        ]
+#if !os(macOS)
+        let session = AVAudioSession.sharedInstance()
+        try session.setCategory(.playAndRecord, mode: .default)
+#endif
+        let recorder = try AVAudioRecorder(url: url, settings: recordSettings)
+        recorder.delegate = delegate
+        if recorder.record() == false {
+            print("Could not start recording")
+            throw RecorderError.couldNotStartRecording
+        }
+        self.recorder = recorder
+    }
+    
+    func stopRecording() {
+        recorder?.stop()
+        recorder = nil
+    }
+}

examples/whisper.swiftui/whisper.swiftui.demo/Utils/RiffWaveUtils.swift

@@ -0,0 +1,12 @@
+import Foundation
+
+func decodeWaveFile(_ url: URL) throws -> [Float] {
+    let data = try Data(contentsOf: url)
+    let floats = stride(from: 44, to: data.count, by: 2).map {
+        return data[$0..<$0 + 2].withUnsafeBytes {
+            let short = Int16(littleEndian: $0.load(as: Int16.self))
+            return max(-1.0, min(Float(short) / 32767.0, 1.0))
+        }
+    }
+    return floats
+}