Binary files in patch always show "no changes"

[eseliger]

In a binary patch, the file content is encoded in the diff either in literal or delta mode. We should add a function to go-diff probably, that allows to retrieve the file content (RFC1924 line-based encoded and zlib compressed, as far as I could reverse engineer).

Note: The first byte in a line is the line length.

Currently, we cannot get the file content, making it appear as an empty file, which has no way to determine it's binary, so "no changes" is shown.

Tasks

• Implement a decodeBinaryDiff function
• Check if is binary diff and use decodeBinaryDiff's return value in here https://sourcegraph.com/github.com/sourcegraph/sourcegraph@f12f17dbd9c2ad735b183a7712beb58993a295b0/-/blob/enterprise/internal/campaigns/resolvers/patch_sets.go#L370