Added copy file path button to diffs

Closes #23108

CHANGELOG

@@ -26,6 +26,7 @@ v 8.13.0 (unreleased)
   - Revert "Label list shows all issues (opened or closed) with that label"
   - Expose expires_at field when sharing project on API
   - Fix VueJS template tags being rendered in code comments
+  - Added copy file path button to merge request diff files
   - Fix issue with page scrolling to top when closing or pinning sidebar (lukehowell)
   - Add Issue Board API support (andrebsguedes)
   - Allow the Koding integration to be configured through the API

app/helpers/button_helper.rb

@@ -15,10 +15,11 @@ module ButtonHelper
   #
   # See http://clipboardjs.com/#usage
   def clipboard_button(data = {})
+    css_class = data[:class] || 'btn-clipboard'
     data = { toggle: 'tooltip', placement: 'bottom', container: 'body' }.merge(data)
     content_tag :button,
       icon('clipboard'),
-      class: "btn btn-clipboard",
+      class: "btn #{css_class}",
       data: data,
       type: :button,
       title: "Copy to Clipboard"

app/views/projects/diffs/_file.html.haml

@@ -8,7 +8,7 @@
           = link_to '#', class: 'js-toggle-diff-comments btn active has-tooltip btn-file-option', title: "Toggle comments for this file", disabled: @diff_notes_disabled do
             = icon('comment')
           \
-
+          = clipboard_button(clipboard_text: diff_file.new_path, class: 'btn-file-option')
           - if editable_diff?(diff_file)
             - link_opts = @merge_request.id ? { from_merge_request_id: @merge_request.id } : {}
             = edit_blob_link(@merge_request.source_project, @merge_request.source_branch, diff_file.new_path,