SnapshotCreator API test v2

[GustavoCaso]

Change snapshot creator API to:

func TestCreateSnapshot(t *testing.T) {
	snapshotCreator := v8.NewSnapshotCreator()
	snapshotCreatorIso := snapshotCreator.GetIsolate()
	snapshotCreatoCtx := v8.NewContext(snapshotCreatorIso)
	defer snapshotCreatoCtx.Close()

	snapshotCreatoCtx.RunScript(`const add = (a, b) => a + b`, "add.js")
	snapshotCreatoCtx.RunScript(`function run() { return add(3, 4); }`, "main.js")
	snapshotCreator.AddContext(snapshotCreatoCtx)

	data, err := snapshotCreator.Create(v8.FunctionCodeHandlingKlear)
	fatalIf(t, err)
        defer data.Dispose()

	iso := v8.NewIsolate(v8.WithStartupData(data))
	defer iso.Dispose()

	ctx := v8.NewContext(iso)
	defer ctx.Close()

	runVal, err := ctx.Global().Get("run")
	if err != nil {
		panic(err)
	}

	fn, err := runVal.AsFunction()
	if err != nil {
		panic(err)
	}
	val, err := fn.Call(v8.Undefined(iso))
	if err != nil {
		panic(err)
	}
	if val.String() != "7" {
		t.Fatal("invalid val")
	}
}