Move context from modules to services (#29440)

Since `modules/context` has to depend on `models` and many other
packages, it should be moved from `modules/context` to
`services/context` according to design principles. There is no logic
code change on this PR, only move packages.

- Move `code.gitea.io/gitea/modules/context` to
`code.gitea.io/gitea/services/context`
- Move `code.gitea.io/gitea/modules/contexttest` to
`code.gitea.io/gitea/services/contexttest` because of depending on
context
- Move `code.gitea.io/gitea/modules/upload` to
`code.gitea.io/gitea/services/context/upload` because of depending on
context

services/context/context_request.go

@@ -0,0 +1,32 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package context
+
+import (
+	"io"
+	"net/http"
+	"strings"
+)
+
+// UploadStream returns the request body or the first form file
+// Only form files need to get closed.
+func (ctx *Context) UploadStream() (rd io.ReadCloser, needToClose bool, err error) {
+	contentType := strings.ToLower(ctx.Req.Header.Get("Content-Type"))
+	if strings.HasPrefix(contentType, "application/x-www-form-urlencoded") || strings.HasPrefix(contentType, "multipart/form-data") {
+		if err := ctx.Req.ParseMultipartForm(32 << 20); err != nil {
+			return nil, false, err
+		}
+		if ctx.Req.MultipartForm.File == nil {
+			return nil, false, http.ErrMissingFile
+		}
+		for _, files := range ctx.Req.MultipartForm.File {
+			if len(files) > 0 {
+				r, err := files[0].Open()
+				return r, true, err
+			}
+		}
+		return nil, false, http.ErrMissingFile
+	}
+	return ctx.Req.Body, false, nil
+}