UTF-16 and UTF-32 files don't show up in the diff (BBCDEV-9261)

Bitbucket renders UTF-

-

files in the source view, but in the diff view it fails. The reason is that git itself treats utf-16,32 as binary.

Implementation notes:

It is possible to use the textconv option when using format-patch (which is what BB uses to generate the diff view), with an option similar to 'iconv -f utf-16 -t utf-8' and hence show a human readable patch.