Fine tune more downdrop settings, use SVG for labels, improve Repo Topic Edit form (#23626)

Although it seems that some different purposes are mixed in this PR,
however, they are all related, and can be tested together, so I put them
together to save everyone's time.

Diff: `+79 −84`, everything becomes much better.

### Improve the dropdown settings.

Move all fomantic-init related code into our `fomantic.js`

Fine-tune some dropdown global settings, see the comments.

Also help to fix the first problem in #23625 , cc: @yp05327 

The "language" menu has been simplified, and it works with small-height
window better.

### Use SVG instead of `<i class="delete icon">`

It's also done by `$.fn.dropdown.settings.templates.label` , cc:
@silverwind

### Remove incorrect `tabable` CSS class

It doesn't have CSS styles, and it was only in Vue. So it's totally
unnecessary, remove it by the way.

### Improve the Repo Topic Edit form

* Simplify the code
* Add a "Cancel" button
* Align elements

Before:

<details>

![image](https://user-images.githubusercontent.com/2114189/223325782-f09532de-0c38-4742-ba86-ed35cc9a858d.png)

</details>

After:

![image](https://user-images.githubusercontent.com/2114189/226796347-207feb0a-b3cd-4820-8a3e-01930bab1069.png)

web_src/js/modules/fomantic.js

@@ -0,0 +1,29 @@
+import $ from 'jquery';
+import {initAriaCheckboxPatch} from './aria/checkbox.js';
+import {initAriaDropdownPatch} from './aria/dropdown.js';
+import {svg} from '../svg.js';
+
+export function initGiteaFomantic() {
+  // Silence fomantic's error logging when tabs are used without a target content element
+  $.fn.tab.settings.silent = true;
+  // Disable the behavior of fomantic to toggle the checkbox when you press enter on a checkbox element.
+  $.fn.checkbox.settings.enableEnterKey = false;
+
+  // Prevent Fomantic from guessing the popup direction.
+  // Otherwise, if the viewport height is small, Fomantic would show the popup upward,
+  // if the dropdown is at the beginning of the page, then the top part would be clipped by the window view, eg: Issue List "Sort" dropdown
+  $.fn.dropdown.settings.direction = 'downward';
+  // By default, use "exact match" for full text search
+  $.fn.dropdown.settings.fullTextSearch = 'exact';
+  // Do not use "cursor: pointer" for dropdown labels
+  $.fn.dropdown.settings.className.label += ' gt-cursor-default';
+  // Always use Gitea's SVG icons
+  $.fn.dropdown.settings.templates.label = function(_value, text, preserveHTML, className) {
+    const escape = $.fn.dropdown.settings.templates.escape;
+    return escape(text, preserveHTML) + svg('octicon-x', 16, `${className.delete} icon`);
+  };
+
+  // Use the patches to improve accessibility, these patches are designed to be as independent as possible, make it easy to modify or remove in the future.
+  initAriaCheckboxPatch();
+  initAriaDropdownPatch();
+}