Stop using getTransform (#950)

* Stop using getTransform

Fixes #861

The original motivation behind this is to make it work with Firefox. But it also helped make the code more intentional.

Test Plan:
- Create one square, select it, zoom in repeatedly, make sure that it zooms centered in the screen and everything looks good
- Scroll at various zoom levels, things look good
- Export a small scene at 1x and 3x, make sure the background is properly set and look good

* fix selection element

src/renderer/renderElement.ts

@@ -303,6 +303,10 @@ export function renderElement(
       context.fillStyle = "rgba(0, 0, 255, 0.10)";
       context.fillRect(0, 0, element.width, element.height);
       context.fillStyle = fillStyle;
+      context.translate(
+        -element.x - sceneState.scrollX,
+        -element.y - sceneState.scrollY,
+      );
       break;
     }
     case "rectangle":