LoroTree toJSON uses `meta` key where `data` would make more sense

[canadaduane]

When working with LoroTree, the API uses node.data to access the node's LoroMap, but toJSON() outputs this as meta:

Example

import { LoroDoc } from "loro-crdt"

const doc = new LoroDoc()
const tree = doc.getTree("tree")

// Create a node
const node = tree.createNode()

// The API uses `.data` to access the node's LoroMap
node.data.set("name", "root")
node.data.set("value", 42)

console.log("API uses .data:", node.data.toJSON())
// Output: { name: "root", value: 42 }

// But toJSON() outputs it as `meta`
console.log("toJSON uses meta:", JSON.stringify(tree.toJSON(), null, 2))

Output:

[
  {
    parent: null,
    index: 0,
    meta: { name: 'root', value: 42 }, <-- "meta" instead of "data"
    id: '0@3781444021239823132',
    fractional_index: '80',
    children: []
  }
]

I think it would be more consistent if the toJSON() output also used data as the key here.

[canadaduane]

I just noticed this related issue: #223

(Mentions using 'data' instead of 'meta')