Refactor/vanilla store utils (#3138)

* feat(stores): use vanilla store utils

* fix(store-utils): keep dimensions if possible

* feat(utils): add nodeDimension and panBy utils

* fix(svelte): use correct updateDim func

* refactor(react): cleanup store

* chore(tests): use new imports

packages/svelte/src/lib/container/Viewport/Viewport.svelte

@@ -5,7 +5,7 @@
 </script>
 
 <div
-  class="svelte-flow__viewport"
+  class="svelte-flow__viewport xyflow__viewport"
   style="transform: translate({$transform[0]}px, {$transform[1]}px) scale({$transform[2]})"
 >
   <slot />