refactor(svelte): cleanup useSvelteFlow, add functions (#3474)

* chore(svelte) removed nodes, edges from useSvelteFlow

* feat(svelte) added deleteElements to useSvelteFlow

* fix(svelte) parent div gets resized correctly, got rid of getBoundingClient Rect

* feat(svelte) added screenToFlowCoordinate

* feat(svelte) added flowToScreenCoordinate to useSvelteFlow

* chore(svelte) removed project from useSvelteFlow

* Delete examples/svelte/src/routes/add-node-on-drop/+server.ts

---------

Co-authored-by: Moritz Klack <info@moritzklack.com>

packages/svelte/src/lib/container/SvelteFlow/SvelteFlow.svelte

@@ -71,13 +71,14 @@
   export { className as class };
 
   let domNode: HTMLDivElement;
+  let clientWidth: number;
+  let clientHeight: number;
 
   const store = hasContext(key) ? useStore() : createStoreContext();
 
   onMount(() => {
-    const { width, height } = domNode.getBoundingClientRect();
-    store.width.set(width);
-    store.height.set(height);
+    store.width.set(clientWidth);
+    store.height.set(clientHeight);
     store.domNode.set(domNode);
 
     store.syncNodeStores(nodes);
@@ -141,6 +142,8 @@
 
 <div
   bind:this={domNode}
+  bind:clientWidth
+  bind:clientHeight
   {style}
   class={cc(['svelte-flow', className])}
   data-testid="svelte-flow__wrapper"