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>

services/context/api.go

@@ -227,7 +227,7 @@ func APIContexter() func(http.Handler) http.Handler {
 
 			ctx.SetContextValue(apiContextKey, ctx)
 
-			// If request sends files, parse them here otherwise the Query() can't be parsed and the CsrfToken will be invalid.
+			// FIXME: GLOBAL-PARSE-FORM: see more details in another FIXME comment
 			if ctx.Req.Method == http.MethodPost && strings.Contains(ctx.Req.Header.Get("Content-Type"), "multipart/form-data") {
 				if !ctx.ParseMultipartForm() {
 					return