[GameTest] .getNBT() and NBTTag class

Minecraft Java Edition has /data command, but Bedrock Edition doesn't have it so we can't modify NBT of items/entities on Bedrock Edition right now.

Syntax: (TypeScript)

ItemStack.getNBT() :NbtTag
Entity.getNBT() :NbtTag

//defines types of NBT tag
enum NbtTagType{
    compound="compound",
    list="list",
    str="string",
    byte="byte",
    short="short",
    int="int",

//JavaScript's number type cannot represent this type accurately, so we have to use BigInt instead
    long="long",

    float="float",
    double="double",

//aliases
    int8="byte",
    int16="short",
    int32="int",
    int64="long",
    float32="float",
    float64="double"
}

//NbtTag class contains informations of NBT tag
//It can contain any type of tag that is in NbtTagType enum

read-only NbtTag.type :NbtTagType

//creates NbtTag object
//type of value must match to tagType argument
//throws error if tag type cannot represent specified value
new NbtTag(tagType :NbtTagType, value :Record<string,NbtTag>|NbtTag[]|string|BigInt|number)

//only valid when NbtTag stores compound data
NbtTag.getKey(keyName :string) :NbtTag|undefined
NbtTag.setKey(keyName :string, value :NbtTag) :NbtTag|undefined
NbtTag.hasKey(keyName :string) :boolean

//sets value of itself
NbtTag.setValue(value :NbtTag) :NbtTag

//returns primitive value of itself
NbtTag.getPrimitiveValue() :Record<string,NbtTag>|NbtTag[]|string|BigInt|number

//path argument contains NBT path
//example: Inventory[{Slot:0b}]
NbtTag.getNbtFromPath(path :string) :NbtTag[]

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