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>

tests/integration/mirror_push_test.go

@@ -79,7 +79,6 @@ func testMirrorPush(t *testing.T, u *url.URL) {
 
 func testCreatePushMirror(t *testing.T, session *TestSession, owner, repo, address, username, password, interval string) {
 	req := NewRequestWithValues(t, "POST", fmt.Sprintf("/%s/%s/settings", url.PathEscape(owner), url.PathEscape(repo)), map[string]string{
-		"_csrf":                GetUserCSRFToken(t, session),
 		"action":               "push-mirror-add",
 		"push_mirror_address":  address,
 		"push_mirror_username": username,
@@ -94,7 +93,6 @@ func testCreatePushMirror(t *testing.T, session *TestSession, owner, repo, addre
 
 func doRemovePushMirror(t *testing.T, session *TestSession, owner, repo string, pushMirrorID int64) bool {
 	req := NewRequestWithValues(t, "POST", fmt.Sprintf("/%s/%s/settings", url.PathEscape(owner), url.PathEscape(repo)), map[string]string{
-		"_csrf":          GetUserCSRFToken(t, session),
 		"action":         "push-mirror-remove",
 		"push_mirror_id": strconv.FormatInt(pushMirrorID, 10),
 	})
@@ -105,7 +103,6 @@ func doRemovePushMirror(t *testing.T, session *TestSession, owner, repo string,
 
 func doUpdatePushMirror(t *testing.T, session *TestSession, owner, repo string, pushMirrorID int64, interval string) bool {
 	req := NewRequestWithValues(t, "POST", fmt.Sprintf("/%s/%s/settings", owner, repo), map[string]string{
-		"_csrf":                  GetUserCSRFToken(t, session),
 		"action":                 "push-mirror-update",
 		"push_mirror_id":         strconv.FormatInt(pushMirrorID, 10),
 		"push_mirror_interval":   interval,