Refactor hiding-methods, remove jQuery show/hide, remove .hide class, remove inline style=display:none (#22950)

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

templates/repo/home.tmpl

@@ -34,7 +34,7 @@
 		</div>
 		{{end}}
 		{{if and .Permission.IsAdmin (not .Repository.IsArchived)}}
-		<div class="ui repo-topic-edit grid form" id="topic_edit" style="display:none">
+		<div class="ui repo-topic-edit grid form gt-hidden" id="topic_edit">
 			<div class="fourteen wide column">
 				<div class="field">
 					<div class="ui fluid multiple search selection dropdown">
@@ -52,7 +52,7 @@
 			</div>
 		</div>
 		{{end}}
-		<div class="hide" id="validate_prompt">
+		<div class="gt-hidden" id="validate_prompt">
 			<span id="count_prompt">{{.locale.Tr "repo.topic.count_prompt"}}</span>
 			<span id="format_prompt">{{.locale.Tr "repo.topic.format_prompt"}}</span>
 		</div>