Fix tooltips and issue dependency styles (#13458)

- Convert all tooltips to JS-based ones, fixing overflow issues
- Restyle issue dependencies/dependants
- Move popup styles to base style
- CSS Helper tweaks
- Unify pseudo element selectors and lint for it

Fixes: https://github.com/go-gitea/gitea/issues/13400

web_src/less/features/animations.less

@@ -12,7 +12,7 @@
   overflow: hidden !important;
 }
 
-.is-loading:after {
+.is-loading::after {
   content: "";
   position: absolute;
   display: block;