[ios] Disable map snapshots by default. This fixes following issues: (#83)

* Map can flash another map style when brought to foreground
* Map can jump when brought to foreground
* Fixed "zoomed in" flash issue with Metal branch (https://github.com/maplibre/maplibre-gl-native/issues/76)

platform/ios/platform/ios/src/MGLMapView.mm

@@ -6699,7 +6699,9 @@ static void *windowScreenContext = &windowScreenContext;
         return;
     }
 
+#ifdef MBGL_ENABLE_MAP_SNAPSHOTS
     [self queueBackgroundSnapshot];
+#endif
 
     if ([self.delegate respondsToSelector:@selector(mapViewDidBecomeIdle:)]) {
         [self.delegate mapViewDidBecomeIdle:self];