This will avoid application errors generated by the assumption of the
presence of these params.

This allows us to take advantage of Rails' `to_partial_path` to render
the correct partial based on the Blob type, rather than cluttering the
view with conditionals.

It also allows (and will allow in the future) better encapsulation for
Blob-related logic which makes sense for our Rails app but might not
make as much sense for the core `gitlab_git` library, such as detecting
if the blob is an SVG.

Now we apply syntax highlighting to the whole old and new files.
This basically help us to highlight adequately multiline content.