[whatwg/streams] How to create a transformed WritableStream that waits for close? (Issue #1222)

Now I have this API:

```ts
export function adbSyncPush(
    stream: AdbBufferedStream,
    writer: WritableStreamDefaultWriter<Uint8Array>,
    filename: string,
    mode: number = (LinuxFileType.File << 12) | 0o666,
    mtime: number = (Date.now() / 1000) | 0,
    packetSize: number = ADB_SYNC_MAX_PACKET_SIZE,
): WritableStream<Uint8Array> {
    // FIXME: `ChunkStream` can't forward `close` Promise.
    const { readable, writable } = new ChunkStream(packetSize);
    readable.pipeTo(new WritableStream<Uint8Array>({
        async start() {
            const pathAndMode = `${filename},${mode.toString()}`;
            await adbSyncWriteRequest(writer, AdbSyncRequestId.Send, pathAndMode);
        },
        async write(chunk) {
            await adbSyncWriteRequest(writer, AdbSyncRequestId.Data, chunk);
        },
        async close() {
            await adbSyncWriteRequest(writer, AdbSyncRequestId.Done, mtime);
            await adbSyncReadResponse(stream, ResponseTypes);
        }
    }, {
        highWaterMark: 16 * 1024,
        size(chunk) { return chunk.byteLength; }
    }));
    return writable;
}
```

It returns a `WrtiableStream` to let the caller write a file on device, the `close` handler tells the device to finish the file and return the final result. Let's call it `PushFileStream`.

Because each packet can't exceed `packetSize` length, I need to split each incoming `chunk`s. I think I can re-use the `ChunkStream` (a `TransformStream`) that's used somewhere else, so I piped the `readable` end to `PushFileStream`, and returned the writable end of the `ChunkStream` to callers.

It can correctly chunk the incoming data and send them to device, however, the `writable` of `ChunkStream` won't wait for `close` of `PushFileStream`. If the caller want to close the `stream` and `writer` after finishing pushing, they may be closed before `close`, causing push to fail.

So how can I wait for `PushFileStream` `close`, or how can I generally use `TransformStream` when creating a `WritableStream`?

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