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/branches_test.go

@@ -61,9 +61,7 @@ func branchAction(t *testing.T, button string) (*HTMLDoc, string) {
 		t.Skip()
 	}
 
-	req = NewRequestWithValues(t, "POST", link, map[string]string{
-		"_csrf": htmlDoc.GetCSRF(),
-	})
+	req = NewRequest(t, "POST", link)
 	session.MakeRequest(t, req, http.StatusOK)
 
 	url, err := url.Parse(link)