Refactor request context (#32956)

Introduce RequestContext: is a short-lived context that is used to store
request-specific data.

RequestContext could be used to clean form tmp files, close context git
repo, and do some tracing in the future.

Then a lot of legacy code could be removed or improved. For example:
most `ctx.Repo.GitRepo.Close()` could be removed because the git repo
could be closed when the request is done.

modules/web/route.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"code.gitea.io/gitea/modules/htmlutil"
+	"code.gitea.io/gitea/modules/reqctx"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/web/middleware"
 
@@ -29,12 +30,12 @@ func Bind[T any](_ T) http.HandlerFunc {
 }
 
 // SetForm set the form object
-func SetForm(dataStore middleware.ContextDataStore, obj any) {
+func SetForm(dataStore reqctx.ContextDataProvider, obj any) {
 	dataStore.GetData()["__form"] = obj
 }
 
 // GetForm returns the validate form information
-func GetForm(dataStore middleware.ContextDataStore) any {
+func GetForm(dataStore reqctx.RequestDataStore) any {
 	return dataStore.GetData()["__form"]
 }