Improve diff expansion text

The previous copy "Show all lines" could be read as showing all
unchanged lines in the entire file, rather than just the unchanged
lines between hunks or file boundary. Replacing 'all' with 'unchanged'
reduces this opportunity for confusion.

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

@@ -226,7 +226,7 @@ export default {
         <icon :size="12" name="expand-up" aria-hidden="true" />
       </a>
       <a class="mx-2 cursor-pointer js-unfold-all" @click="handleExpandLines()">
-        <span>{{ s__('Diffs|Show all lines') }}</span>
+        <span>{{ s__('Diffs|Show unchanged lines') }}</span>
       </a>
       <a
         v-if="canExpandDown"

changelogs/unreleased/feature-jramsay-diff-expansion-copy.yml

+---
+title: Improve diff expansion text
+merge_request: 21616
+author:
+type: other

doc/user/project/merge_requests/reviewing_and_managing_merge_requests.md

@@ -68,7 +68,7 @@ list.
 
 By default, the diff shows only the parts of a file which are changed.
 To view more unchanged lines above or below a change click on the
-**Expand up** or **Expand down** icons. You can also click on **Show all lines**
+**Expand up** or **Expand down** icons. You can also click on **Show unchanged lines**
 to expand the entire file.
 
 ![Incrementally expand merge request diffs](img/incrementally_expand_merge_request_diffs_v12_2.png)

locale/gitlab.pot

@@ -5988,7 +5988,7 @@ msgstr ""
 msgid "Diffs|No file name available"
 msgstr ""
 
-msgid "Diffs|Show all lines"
+msgid "Diffs|Show unchanged lines"
 msgstr ""
 
 msgid "Diffs|Something went wrong while fetching diff lines."