Fix heatmap/image traces without zsmooth on Safari/iOS

draftlogs/6605_fix.md

@@ -0,0 +1 @@
+ - Fix heatmap rendering on Safari when `zsmooth` is set to false [[#6605](https://github.com/plotly/plotly.js/pull/6605)], with thanks to @lvlte for the contribution!

src/lib/supports_pixelated_image.js

@@ -15,7 +15,8 @@ function supportsPixelatedImage() {
     if(_supportsPixelated !== null) { // only run the feature detection once
         return _supportsPixelated;
     }
-    if(Lib.isIE()) {
+    if(Lib.isIE() || Lib.isSafari() || Lib.isIOS()) {
+        // NB. Safari passes the test below but the final rendering is not pixelated
         _supportsPixelated = false;
     } else {
         var declarations = Array.from(constants.CSS_DECLARATIONS).reverse();