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/middleware/data.go

@@ -7,46 +7,21 @@ import (
 	"context"
 	"time"
 
+	"code.gitea.io/gitea/modules/reqctx"
 	"code.gitea.io/gitea/modules/setting"
 )
 
-// ContextDataStore represents a data store
-type ContextDataStore interface {
-	GetData() ContextData
-}
-
-type ContextData map[string]any
-
-func (ds ContextData) GetData() ContextData {
-	return ds
-}
-
-func (ds ContextData) MergeFrom(other ContextData) ContextData {
-	for k, v := range other {
-		ds[k] = v
-	}
-	return ds
-}
-
 const ContextDataKeySignedUser = "SignedUser"
 
-type contextDataKeyType struct{}
-
-var contextDataKey contextDataKeyType
-
-func WithContextData(c context.Context) context.Context {
-	return context.WithValue(c, contextDataKey, make(ContextData, 10))
-}
-
-func GetContextData(c context.Context) ContextData {
-	if ds, ok := c.Value(contextDataKey).(ContextData); ok {
-		return ds
+func GetContextData(c context.Context) reqctx.ContextData {
+	if rc := reqctx.GetRequestDataStore(c); rc != nil {
+		return rc.GetData()
 	}
 	return nil
 }
 
-func CommonTemplateContextData() ContextData {
-	return ContextData{
+func CommonTemplateContextData() reqctx.ContextData {
+	return reqctx.ContextData{
 		"IsLandingPageOrganizations": setting.LandingPageURL == setting.LandingPageOrganizations,
 
 		"ShowRegistrationButton":        setting.Service.ShowRegistrationButton,

modules/web/middleware/flash.go

@@ -7,11 +7,13 @@ import (
 	"fmt"
 	"html/template"
 	"net/url"
+
+	"code.gitea.io/gitea/modules/reqctx"
 )
 
 // Flash represents a one time data transfer between two requests.
 type Flash struct {
-	DataStore ContextDataStore
+	DataStore reqctx.RequestDataStore
 	url.Values
 	ErrorMsg, WarningMsg, InfoMsg, SuccessMsg string
 }