feat(obj): allow to create child obj inside property table

[XuNeo]

This patch allows to create child obj directly in the property table. To make it looks like children are created recursively.

In fact, with this coding style, the children is created firstly and it's stored to property table with integer key. Simply find them out and set parent for them.

local lvgl = require("lvgl")

local root = lvgl.Object(nil, {
    flex = {
        flex_direction = "row",
        flex_wrap = "wrap",
        justify_content = "center",
        align_items = "center",
        align_content = "center",
    },
    w = 300,
    h = 75,
    align = lvgl.ALIGN.CENTER,
    lvgl.Object(nil, {
        w = 100,
        h = lvgl.PCT(100),
        lvgl.Label(nil, {
            text = string.format("label %d", 1)
        }):center()
    }):clear_flag(lvgl.FLAG.SCROLLABLE),

    lvgl.Object(nil, {
        w = 100,
        h = lvgl.PCT(100),
        lvgl.Label(nil, {
            text = string.format("label %d", 1)
        }):center()
    }):clear_flag(lvgl.FLAG.SCROLLABLE)
})