fix(liveness): center camera preview (#50)

Author: eeatonaws

liveness/src/main/java/com/amplifyframework/ui/liveness/ui/FaceLivenessDetector.kt

@@ -185,12 +185,18 @@ internal fun ChallengeView(
         val videoViewportSize = livenessState.videoViewportSize
 
         if (videoViewportSize != null) {
-            AndroidView(
-                { livenessCoordinator.previewTextureView },
-                Modifier
+            Box(
+                modifier = Modifier
                     .size(videoViewportSize.viewportDpSize)
                     .align(Alignment.Center)
-            )
+            ) {
+                AndroidView(
+                    { livenessCoordinator.previewTextureView },
+                    Modifier
+                        .size(videoViewportSize.viewportDpSize)
+                        .align(Alignment.Center)
+                )
+            }
 
             livenessState.faceGuideRect?.let {
                 FaceGuide(