Multiple improvements for comment edit diff (#21990)

- Use explicit avatar size so when JS copies the HTML, the size gets
copied with it
- Replace icon font use with SVG
- Improve styling and diff rendering
- Sort lists in `svg.js`

Fixes: https://github.com/go-gitea/gitea/issues/21924

<img width="933" alt="Screenshot 2022-11-30 at 17 52 17"
src="https://user-images.githubusercontent.com/115237/204859608-f322a8f8-7b91-45e4-87c0-82694e574115.png">

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/less/_repository.less

@@ -2963,6 +2963,24 @@ tbody.commit-list {
   text-align: left;
 }
 
+.comment-diff-data {
+  background: var(--color-code-bg);
+  max-height: calc(100vh - 10.5rem);
+  overflow-y: auto;
+}
+
+.comment-diff-data pre {
+  line-height: 18px;
+  white-space: pre-wrap;
+  word-break: break-all;
+  overflow-wrap: break-word;
+}
+
+.content-history-detail-dialog .header .avatar {
+  position: relative;
+  top: -2px;
+}
+
 #topic_edit {
   margin-top: 5px;
 }