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/repo_generate_test.go

@@ -44,7 +44,6 @@ func testRepoGenerate(t *testing.T, session *TestSession, templateID, templateOw
 	_, exists = htmlDoc.doc.Find(fmt.Sprintf(`#repo_owner_dropdown .item[data-value="%d"]`, generateOwner.ID)).Attr("data-value")
 	assert.True(t, exists, "Generate owner '%s' is not present in select box", generateOwnerName)
 	req = NewRequestWithValues(t, "POST", link, map[string]string{
-		"_csrf":         htmlDoc.GetCSRF(),
 		"uid":           strconv.FormatInt(generateOwner.ID, 10),
 		"repo_name":     generateRepoName,
 		"repo_template": templateID,