Start cleaning the messy ".ui.left / .ui.right", improve label list page, fix stackable menu (#24393)

Since 2015/2016, there is a global pollution: ".ui.left" / ".ui.right".

Fomantic UI doesn't work this way, it just conflicts with many Fomantic
definitions.

This PR starts the cleaning work of such techinical debts.

And, the "label list" page has been quite messy for long time, for
example, why "li" appears in "div" ......

And fix #24296

<details>


![image](https://user-images.githubusercontent.com/2114189/235051281-54c5374c-b5fd-4b5f-9aa2-02d4bb2d9112.png)


![image](https://user-images.githubusercontent.com/2114189/235055703-2ba042e0-4db7-4e63-8646-02f390d496b5.png)


![image](https://user-images.githubusercontent.com/2114189/235056310-4f6ffdc2-5758-4927-8fb8-314d9fb72a6b.png)


![image](https://user-images.githubusercontent.com/2114189/235058400-dab1c9ec-3325-4671-8345-aee6b0b68042.png)


![image](https://user-images.githubusercontent.com/2114189/235058424-85509532-b9bc-43ad-b00f-a87184c60f22.png)

</details>

templates/repo/diff/conversation.tmpl

@@ -9,11 +9,11 @@
 				<b>{{$resolveDoer.Name}}</b> {{$.locale.Tr "repo.issues.review.resolved_by"}}
 			</div>
 			<div>
-				<button id="show-outdated-{{(index .comments 0).ID}}" data-comment="{{(index .comments 0).ID}}" class="ui tiny right labeled button show-outdated gt-df gt-ac">
+				<button id="show-outdated-{{(index .comments 0).ID}}" data-comment="{{(index .comments 0).ID}}" class="ui tiny labeled button show-outdated gt-df gt-ac">
 					{{svg "octicon-unfold" 16 "gt-mr-3"}}
 					{{$.locale.Tr "repo.issues.review.show_resolved"}}
 				</button>
-				<button id="hide-outdated-{{(index .comments 0).ID}}" data-comment="{{(index .comments 0).ID}}" class="ui tiny right labeled button hide-outdated gt-df gt-ac gt-hidden">
+				<button id="hide-outdated-{{(index .comments 0).ID}}" data-comment="{{(index .comments 0).ID}}" class="ui tiny labeled button hide-outdated gt-df gt-ac gt-hidden">
 					{{svg "octicon-fold" 16 "gt-mr-3"}}
 					{{$.locale.Tr "repo.issues.review.hide_resolved"}}
 				</button>