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/settings/webhook/history.tmpl

@@ -25,7 +25,7 @@
 							</span>
 						</div>
 					</div>
-					<div class="info hide" id="info-{{.ID}}">
+					<div class="info gt-hidden" id="info-{{.ID}}">
 						<div class="ui top attached tabular menu">
 							<a class="item active" data-tab="request-{{.ID}}">{{$.locale.Tr "repo.settings.webhook.request"}}</a>
 							<a class="item" data-tab="response-{{.ID}}">

templates/repo/settings/webhook/settings.tmpl

@@ -22,7 +22,7 @@
 		</div>
 	</div>
 
-	<div class="events fields ui grid" {{if not .Webhook.ChooseEvents}}style="display:none"{{end}}>
+	<div class="events fields ui grid {{if not .Webhook.ChooseEvents}}gt-hidden{{end}}">
 		<!-- Repository Events -->
 		<div class="fourteen wide column">
 			<label>{{.locale.Tr "repo.settings.event_header_repository"}}</label>