refactor(editor): extract root block (#10356)

Closes: [BS-2207](https://linear.app/affine-design/issue/BS-2207/move-root-block-to-affineblock-root)

blocksuite/affine/block-root/src/edgeless/utils/bound-utils.ts

@@ -0,0 +1,38 @@
+import type { SerializedElement } from '@blocksuite/block-std/gfx';
+import { Bound, getBoundWithRotation } from '@blocksuite/global/utils';
+import { type BlockSnapshot, BlockSnapshotSchema } from '@blocksuite/store';
+
+export function getBoundFromSerializedElement(element: SerializedElement) {
+  return Bound.from(
+    getBoundWithRotation({
+      ...Bound.deserialize(element.xywh),
+      rotate: typeof element.rotate === 'number' ? element.rotate : 0,
+    })
+  );
+}
+
+export function getBoundFromGfxBlockSnapshot(snapshot: BlockSnapshot) {
+  if (typeof snapshot.props.xywh !== 'string') return null;
+  return Bound.deserialize(snapshot.props.xywh);
+}
+
+export function edgelessElementsBoundFromRawData(
+  elementsRawData: (SerializedElement | BlockSnapshot)[]
+) {
+  if (elementsRawData.length === 0) return new Bound();
+
+  let prev: Bound | null = null;
+
+  for (const data of elementsRawData) {
+    const { data: blockSnapshot } = BlockSnapshotSchema.safeParse(data);
+    const bound = blockSnapshot
+      ? getBoundFromGfxBlockSnapshot(blockSnapshot)
+      : getBoundFromSerializedElement(data as SerializedElement);
+
+    if (!bound) continue;
+    if (!prev) prev = bound;
+    else prev = prev.unite(bound);
+  }
+
+  return prev ?? new Bound();
+}