Allow bsdiff to accept multiple compressors

We modified the patch writer to have the capability to produce the smallest
patch if multiple compressors are given. This type is supported for bsdf2
format only.

Example usage:
bsdiff --format=bsdf2 --type=bz2:brotli <src_file> <tgt_file> <patch_file>

Test: diff & patch an apk file

Change-Id: Icd4322f21975b82c5ee09f8feb9321f52c9813a4