[BUG]: B3DMLoader/I3DMLoader 不必要内存开销

[jiangheng90]

Bug描述

B3DMLoaderBase和I3DMLoaderBase中使用buffer.slice对原有内存的拷贝
以对FeatureTable的构造为例其中一段代码

const featureTableStart = 28;
const featureTableBuffer = buffer.slice(
    featureTableStart,
    featureTableStart + featureTableJSONByteLength + featureTableBinaryByteLength,
);
const featureTable = new FeatureTable(
    featureTableBuffer,
    0,
    featureTableJSONByteLength,
    featureTableBinaryByteLength,
);

该部分会产生额外的内存开销

在3DTiles的大规模数据渲染实践中内存是非常宝贵的系统资源，引用一小段cesium 106版本对于featureTable的处理

let featureTableJson;
if (featureTableJsonByteLength === 0) {
  featureTableJson = {
    BATCH_LENGTH: defaultValue(batchLength, 0),
  };
} else {
  featureTableJson = getJsonFromTypedArray(
    uint8Array,
    byteOffset,
    featureTableJsonByteLength
  );
  byteOffset += featureTableJsonByteLength;
}

const featureTableBinary = new Uint8Array(
  arrayBuffer,
  byteOffset,
  featureTableBinaryByteLength
);
byteOffset += featureTableBinaryByteLength;

其中arraybuffer是直接来自下载数据