function readPlainByteArrayFixed(reader, count, fixedLength) {
  // assert(reader.view.byteLength - reader.offset >= count * fixedLength)
  const values = new Array(count)
  for (let i = 0; i < count; i++) {
    values[i] = new Uint8Array(reader.view.buffer, reader.view.byteOffset + reader.offset, fixedLength)
    reader.offset += fixedLength
  }
  return values
}
Read a fixed length byte array.

@param {DataReader} reader
@param {number} count
@param {number} fixedLength
@returns {Uint8Array[]}