Get a buffer with the filtered content of a blob.

This applies filters as if the blob was being checked out to the working directory under the specified filename. This may apply CRLF filtering or other types of changes depending on the file attributes set for the blob and the content detected in it.

The output is written into a git_buf which the caller must free when done (via git_buf_free).

If no filters need to be applied, then the out buffer will just be populated with a pointer to the raw content of the blob. In that case, be careful to not free the blob until done with the buffer or copy it into memory you own.