Migrate gt-hidden to tw-hidden (#30046)

We have to define this one in helpers.css because tailwind only
generates a single class but certain things rely on this being
double-class. Command ran:

```sh
perl -p -i -e 's#gt-hidden#tw-hidden#g' web_src/js/**/* templates/**/* models/**/* web_src/css/**/*

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
(cherry picked from commit ec3d467f15a683b305ac165c3eba6683628dcb25)

Conflicts:
	templates/install.tmpl
	templates/repo/diff/conversation.tmpl
	templates/repo/issue/view_content/conversation.tmpl
	templates/repo/issue/view_content/sidebar.tmpl
	templates/repo/issue/view_title.tmpl

	resolved by prefering Forgejo version and applying the
	commands to all files

tailwind.config.js

@@ -41,6 +41,8 @@ export default {
     // classes that don't work without CSS variables from "@tailwind base" which we don't use
     'transform', 'shadow', 'ring', 'blur', 'grayscale', 'invert', '!invert', 'filter', '!filter',
     'backdrop-filter',
+    // we use double-class tw-hidden defined in web_src/css/helpers.css for increased specificity
+    'hidden',
     // unneeded classes
     '[-a-zA-Z:0-9_.]',
   ],