Close #22847
This PR:
* introduce Gitea's own `showElem` and related functions
* remove jQuery show/hide
* remove .hide class
* remove inline style=display:none
From now on:
do not use:
* "[hidden]" attribute: it's too weak, can not be applied to an element
with "display: flex"
* ".hidden" class: it has been polluted by Fomantic UI in many cases
* inline style="display: none": it's difficult to tweak
* jQuery's show/hide/toggle: it can not show/hide elements with
"display: xxx !important"
only use:
* this ".gt-hidden" class
* showElem/hideElem/toggleElem functions in "utils/dom.js"
cc: @silverwind , this is the all-in-one PR
