compress/decompress the truncated JPEG image

[zuoerfeng]

pull request: add the function: compress/decompress the truncated JPEG image

what is truncated JPEG image? A：if there is a large jpeg image, it need to stored in two place, so it's truncated into two parts. First part has jpeg header, the second does not. The first part is called truncated JPEG image.

Main steps：

1. find truncated point in read jpeg step
2. add ExternalSection Tag to save the field metadata of the truncated point in brunsli encode step
3. playback the truncated point when decompress brn
4. fill the tail data into jpeg data in write jpeg step

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