iOS: Tweak autofocus settings

- Disable face-driven autofocus on iOS 15.4+
- Enable continuous autofocus if available

+## NEXT
+
+Improvements:
+* [iOS] No longer automatically focus on faces
+
 ## 3.0.0
 This big release contains all improvements from the beta releases.
 In addition to that, this release contains:

@@ -133,6 +133,17 @@ public class MobileScanner: NSObject, AVCaptureVideoDataOutputSampleBufferDelega
         }
 
         device.addObserver(self, forKeyPath: #keyPath(AVCaptureDevice.torchMode), options: .new, context: nil)
+        do {
+            try device.lockForConfiguration()
+            if device.isFocusModeSupported(focusMode: .continuousAutoFocus) {
+                device.focusMode = .continuousAutoFocus
+            }
+            if #available(iOS 15.4, *) {
+                device.automaticallyAdjustsFaceDrivenAutoFocusEnabled = false
+            }
+            device.unlockForConfiguration()
+        } catch {}
+
         captureSession.beginConfiguration()
 
         // Add device input