feat(component): helper function observeResize to observe size change via global ResizeObserver (#7241)

```ts
import { observeResize } from "@affine/component";

useEffect(() => {
  const dispose = observeResize(element entry => {
    console.log(entry.contentRect);
  });

  return () => dispose();
}, []);
```

packages/frontend/component/src/index.ts

@@ -24,3 +24,4 @@ export * from './ui/switch';
 export * from './ui/table';
 export * from './ui/toast';
 export * from './ui/tooltip';
+export * from './utils';

packages/frontend/component/src/ui/date-picker/week-date-picker.tsx

@@ -13,6 +13,7 @@ import {
   useState,
 } from 'react';
 
+import { observeResize } from '../../utils';
 import { IconButton } from '../button';
 import * as styles from './week-date-picker.css';
 
@@ -116,8 +117,7 @@ export const WeekDatePicker = memo(function WeekDatePicker({
     const el = weekRef.current;
     if (!el) return;
 
-    const resizeObserver = new ResizeObserver(entries => {
-      const rect = entries[0].contentRect;
+    return observeResize(el, ({ contentRect: rect }) => {
       const width = rect.width;
       if (!width) return;
 
@@ -127,11 +127,6 @@ export const WeekDatePicker = memo(function WeekDatePicker({
       setViewPortSize(Math.max(1, Math.min(viewPortCount, 7)));
       setDense(width < 300);
     });
-    resizeObserver.observe(el);
-
-    return () => {
-      resizeObserver.disconnect();
-    };
   }, []);
 
   // when value changes, reset cursor

packages/frontend/component/src/utils/index.ts

@@ -0,0 +1 @@
+export * from './observe-resize';

packages/frontend/component/src/utils/observe-resize.ts

@@ -0,0 +1,77 @@
+import type { ResizeObserverEntry } from '@juggle/resize-observer';
+
+type ObserveResize = {
+  callback: (entity: ResizeObserverEntry) => void;
+  dispose: () => void;
+};
+
+let _resizeObserver: ResizeObserver | null = null;
+const elementsMap = new WeakMap<Element, Array<ObserveResize>>();
+
+// for debugging
+(window as any)._resizeObserverElementsMap = elementsMap;
+
+/**
+ * @internal get or initialize the ResizeObserver instance
+ */
+const getResizeObserver = () =>
+  (_resizeObserver ??= new ResizeObserver(entries => {
+    entries.forEach(entry => {
+      const listeners = elementsMap.get(entry.target) ?? [];
+      listeners.forEach(({ callback }) => callback(entry));
+    });
+  }));
+
+/**
+ * @internal remove element's specific listener
+ */
+const removeListener = (element: Element, listener: ObserveResize) => {
+  if (!element) return;
+  const listeners = elementsMap.get(element) ?? [];
+  const observer = getResizeObserver();
+  // remove the listener from the element
+  if (listeners.includes(listener)) {
+    elementsMap.set(
+      element,
+      listeners.filter(l => l !== listener)
+    );
+  }
+  // if no more listeners, unobserve the element
+  if (elementsMap.get(element)?.length === 0) {
+    observer.unobserve(element);
+    elementsMap.delete(element);
+  }
+};
+
+/**
+ * A function to observe the resize of an element use global ResizeObserver.
+ *
+ * ```ts
+ * useEffect(() => {
+ *  const dispose1 = observeResize(elRef1.current, (entry) => {});
+ *  const dispose2 = observeResize(elRef2.current, (entry) => {});
+ *
+ *  return () => {
+ *   dispose1();
+ *   dispose2();
+ *  };
+ * }, [])
+ * ```
+ * @return A function to dispose the observer.
+ */
+export const observeResize = (
+  element: Element,
+  callback: ObserveResize['callback']
+) => {
+  const observer = getResizeObserver();
+  if (!elementsMap.has(element)) {
+    observer.observe(element);
+  }
+  const prevListeners = elementsMap.get(element) ?? [];
+  const listener = { callback, dispose: () => {} };
+  listener.dispose = () => removeListener(element, listener);
+
+  elementsMap.set(element, [...prevListeners, listener]);
+
+  return listener.dispose;
+};