Feature request: A useLayoutEffect with read/write batching across a tree

Today, `useLayoutEffect` can be used for synchronous read/writes across the DOM. ```javascript useLayoutEffect(() => { // Write ref.current.style.transform = "" // Read const box = ref.current.getBoundingClientRect() }) ``` For a single instance of a single component, this works well. But if this code is repeated or reused anywhere in the tree, we trigger [layout thrashing](https://developers.google.com/web/fundamentals/performance/rendering/avoid-large-complex-layouts-and-layout-thrashing). The severity of the layout thrashing scales linearly with the number of hooks/components featuring either this code or code like it. Hooks and components are designed to be composable, yet it's this trivial to write one that isn't. Instead, what I'd like is a batched version of `useLayoutEffect` that provides `read` and `write` callbacks. These schedule callbacks that will be called: 1. Synchronously before paint 2. In "parallel" in reads/writes/reads etc 3. After all child components in the tree have run `useLayoutEffect` - including those entering the tree (currently these don't mount until after other `useLayoutEffect`s have been called) It could look like this, though I'm more interested in the above specs than actual API: ```javascript useBatchedLayoutEffect((read, write) => { write(() => { ref.current.style.transform = "" }) read(() => { const box = ref.current.getBoundingClientRect() }) }) ``` Then, adhering the 3 specifications above, these callbacks are executed in order, so all `read`s from across the tree, then all `write`s, then all `read`s etc. There is no upper limit for the number of permitted ping-ponged reads/writes IMO as the amount of layout thrashing you could possibly suffer will never be worse than the single hungriest hook. In my experience I've never needed more than a read/write/read/write. ## Measurement accuracy In the given example, we're measuring a component after first resetting its `transform` because we want to snapshot…