MR Diffs `endpoint_diff_for_path` doesn't include params

When an MR loads, the page returns endpoint_diff_for_path.
This endpoint is used to fetch single-file diffs when the View one file at a time checkbox is checked, also known as "File-by-File mode."

The diff_for_path_namespace_project_merge_request_path call that populates endpoint_diff_for_path does not include params, which leads to a number of issues including:

• No support for toggling show/hide whitespace
• No support for version diffs other than base/head

The helper method diff_for_path_namespace_project_merge_request_path should be updated to accept arbitrary params like the batch files endpoint, and the diff_for_path_namespace_project_merge_request_path call that populates endpoint_diff_for_path should be updated to include params.