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/oauth_test.go

@@ -92,7 +92,6 @@ func TestAuthorizeShow(t *testing.T) {
 
 	htmlDoc := NewHTMLParser(t, resp.Body)
 	AssertHTMLElement(t, htmlDoc, "#authorize-app", true)
-	htmlDoc.GetCSRF()
 }
 
 func TestAuthorizeRedirectWithExistingGrant(t *testing.T) {