Split "modules/context.go" to separate files (#24569)

The "modules/context.go" is too large to maintain.

This PR splits it to separate files, eg: context_request.go,
context_response.go, context_serve.go

This PR will help:

1. The future refactoring for Gitea's web context (eg: simplify the context)
2. Introduce proper "range request" support
3. Introduce context function

This PR only moves code, doesn't change any logic.

Author: wxiaoguang

models/repo.go

@@ -35,9 +35,6 @@ import (
 	"xorm.io/builder"
 )
 
-// ItemsPerPage maximum items per page in forks, watchers and stars of a repo
-var ItemsPerPage = 40
-
 // Init initialize model
 func Init(ctx context.Context) error {
 	if err := unit.LoadUnitConfig(); err != nil {

models/repo/search.go

@@ -0,0 +1,24 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package repo
+
+import "code.gitea.io/gitea/models/db"
+
+// SearchOrderByMap represents all possible search order
+var SearchOrderByMap = map[string]map[string]db.SearchOrderBy{
+	"asc": {
+		"alpha":   db.SearchOrderByAlphabetically,
+		"created": db.SearchOrderByOldest,
+		"updated": db.SearchOrderByLeastUpdated,
+		"size":    db.SearchOrderBySize,
+		"id":      db.SearchOrderByID,
+	},
+	"desc": {
+		"alpha":   db.SearchOrderByAlphabeticallyReverse,
+		"created": db.SearchOrderByNewest,
+		"updated": db.SearchOrderByRecentUpdated,
+		"size":    db.SearchOrderBySizeReverse,
+		"id":      db.SearchOrderByIDReverse,
+	},
+}