refactor: external render (#38885) (#38898)

Backport #38885 by @wxiaoguang

make the "command variable replacement" more accurate and
OS-independent, add a test for it.

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/common/markup.go

@@ -64,6 +64,7 @@ func RenderMarkup(ctx *context.Base, ctxRepo *context.Repository, mode, text, ur
 		treePath = path.Dir(filePath)                       // it is "doc" if filePath is "doc/CHANGE.md"
 		refPath = strings.Join(fields[3:], "/")             // it is "branch/features/feat-12/doc"
 		refPath = strings.TrimSuffix(refPath, "/"+treePath) // now we get the correct branch path: "branch/features/feat-12"
+		refPath = util.PathEscapeSegments(refPath)
 	} else if fields = strings.SplitN(repoLinkPath, "/", 3); len(fields) == 2 {
 		repoOwnerName, repoName = fields[0], fields[1]
 	}