Replace CSRF cookie with CrossOriginProtection (#36183)

Removes the CSRF cookie in favor of
[`CrossOriginProtection`](https://pkg.go.dev/net/http#CrossOriginProtection)
which relies purely on HTTP headers.

Fixes: https://github.com/go-gitea/gitea/issues/11188
Fixes: https://github.com/go-gitea/gitea/issues/30333
Helps: https://github.com/go-gitea/gitea/issues/35107

TODOs:

- [x] Fix tests
- [ ] Ideally add tests to validates the protection

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/user/settings/security/openid.tmpl

@@ -16,7 +16,6 @@
 				</div>
 				<div class="flex-item-trailing">
 					<form action="{{AppSubUrl}}/user/settings/security/openid/toggle_visibility" method="post">
-						{{$.CsrfTokenHtml}}
 						<input name="id" type="hidden" value="{{.ID}}">
 						{{if .Show}}
 							<button class="ui tiny button">
@@ -40,7 +39,6 @@
 </div>
 <div class="ui bottom attached segment">
 	<form class="ui form" action="{{AppSubUrl}}/user/settings/security/openid" method="post">
-		{{.CsrfTokenHtml}}
 		<div class="required field {{if .Err_OpenID}}error{{end}}">
 			<label for="openid">{{ctx.Locale.Tr "settings.add_new_openid"}}</label>
 			<input id="openid" name="openid" type="text" required>

templates/user/settings/security/twofa.tmpl

@@ -6,12 +6,10 @@
 	{{if .TOTPEnrolled}}
 	<p>{{ctx.Locale.Tr "settings.twofa_is_enrolled"}}</p>
 	<form class="ui form" action="{{AppSubUrl}}/user/settings/security/two_factor/regenerate_scratch" method="post" enctype="multipart/form-data">
-		{{.CsrfTokenHtml}}
 		<p>{{ctx.Locale.Tr "settings.regenerate_scratch_token_desc"}}</p>
 		<button class="ui primary button">{{ctx.Locale.Tr "settings.twofa_scratch_token_regenerate"}}</button>
 	</form>
 	<form class="ui form" action="{{AppSubUrl}}/user/settings/security/two_factor/disable" method="post" enctype="multipart/form-data" id="disable-form">
-		{{.CsrfTokenHtml}}
 		<p>{{ctx.Locale.Tr "settings.twofa_disable_note"}}</p>
 		<button class="ui red button delete-button" data-modal-id="disable-twofa" data-type="form" data-form="#disable-form">{{ctx.Locale.Tr "settings.twofa_disable"}}</button>
 	</form>

templates/user/settings/security/twofa_enroll.tmpl

@@ -9,7 +9,6 @@
 			<p>{{ctx.Locale.Tr "settings.or_enter_secret" .TwofaSecret}}</p>
 			<p>{{ctx.Locale.Tr "settings.then_enter_passcode"}}</p>
 			<form class="ui form" action="{{.Link}}" method="post">
-				{{.CsrfTokenHtml}}
 				<div class="inline required field {{if .Err_Passcode}}error{{end}}">
 					<label for="passcode">{{ctx.Locale.Tr "passcode"}}</label>
 					<input id="passcode" name="passcode" autofocus required>