Clarify "text-align" CSS helpers, fix clone button padding (#25763)

Changes:

* Rename gt-tl/gt-tc/gt-tr to gt-text-left/gt-text-center/gt-text-right
* The gt-ab and gt-br-0 are removed because they are not needed anymore
* Fix the clone dropdown button padding by ":not(.icon)"

Before:

<details>


![image](https://github.com/go-gitea/gitea/assets/2114189/eb030633-622c-4ca7-8e88-ce010d9f51a6)

</details>

After:

<details>


![image](https://github.com/go-gitea/gitea/assets/2114189/64c09403-bf21-439c-88f1-780b34ccab6b)

</details>

Fixes #25758

Co-authored-by: Giteabot <teabot@gitea.io>

web_src/js/features/repo-issue-content.js

@@ -24,7 +24,7 @@ function showContentHistoryDetail(issueBaseUrl, commentId, historyId, itemTitleH
       </div>
     </div>
   </div>
-  <div class="comment-diff-data gt-tl gt-p-3 is-loading"></div>
+  <div class="comment-diff-data gt-text-left gt-p-3 is-loading"></div>
 </div>`);
   $dialog.appendTo($('body'));
   $dialog.find('.dialog-header-options').dropdown({