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

* Add SwiftUI demo project.

* Add -DGGML_USE_ACCELERATE

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
+}