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/common-global.js

@@ -237,7 +237,7 @@ export function initGlobalDropzone() {
           // Create a "Copy Link" element, to conveniently copy the image
           // or file link as Markdown to the clipboard
           const copyLinkElement = document.createElement('div');
-          copyLinkElement.className = 'gt-tc';
+          copyLinkElement.className = 'gt-text-center';
           // The a element has a hardcoded cursor: pointer because the default is overridden by .dropzone
           copyLinkElement.innerHTML = `<a href="#" style="cursor: pointer;">${svg('octicon-copy', 14, 'copy link')} Copy link</a>`;
           copyLinkElement.addEventListener('click', (e) => {