Replaced external link button with doc-text icon

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/59034

app/assets/javascripts/diffs/components/diff_file_header.vue

@@ -303,7 +303,7 @@ export default {
           class="view-file js-view-file-button"
           :title="viewFileButtonText"
         >
-          <icon name="external-link" />
+          <icon name="doc-text" />
         </gl-button>
 
         <a

changelogs/unreleased/59034-external-link-button.yml

+---
+title: Replaced icon for external URL with doc-text icon
+merge_request: 27365
+author:
+type: fixed