Right now, the following naming scheme for diff files is used: diff-1, diff-2, ... and also we have "internal" format which is file-path-HASH, where HASH is sha1 of file path.
Besides, we have HASH_lineA_lineB format to link exact line number in MR diff. It makes sence to unify the way we link diff from outside, while leave "file-path-HASH" format for internal (js) usage.
Changes in this commit  allow to link diff just by HASH, if we don't want specify exact lines, also it changes "file-path-HASH" and "diff-NUMBER" links in code to this unified format.

Inspired by #24010 and !7298

see #22343 for issue description

Magic Variable - Change the name of the variable to assign the local variable for partial, rather than `i` use the `index`.

Don't pass a local variable called `i` to a partial.

So we have raw_diffs too

This object will manage Gitlab::Git::Compare instances

Introducing the concept of SafeDiffs which relates 
diffs with UI highlighting.

We can't reuse the existing value of the format parameter, because on
the merge request page that's 'json', so the link would go to a JSON
file. We can't set it to HTML, because that adds '.html' the URL, which
breaks the compare view (and looks bad). Setting it to nil uses the
default format, which in all of these cases is HTML anyway.

This reverts commit 13e37a3e.

Here was the problem:

1. When determining whether a given blob is viewable text, gitlab_git reads the first 1024 bytes and checks with Linguist whether it is a text or binary file.
2. If the blob is text, GitLab will attempt to display it.
3. However, if the text has binary characters after the first 1024 bytes, then GitLab will attempt to load the entire contents, but the encoding will be ASCII-8BIT since there are binary characters.
4. The Error 500 results when GitLab attempts to display a mix UTF-8 and ASCII-8BIT.

To fix this, we load as much data as we are willing to display so that the detection will work properly. Requires
an update to gitlab_git: gitlab-org/gitlab_git!86

Closes #13826

added whitespace toggle to diffs page and set it to return the project compare path with the selected whitespace params

Updated CHANGELOG

Moved CHANGELOG entry

Closes #3769

Closes #14327

* Use commit objects instead of IDs when generating diffs
* Use proper references when generating MR's source and target
* Update broken specs

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

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