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