Refactor packages (func name & UI) (#34773)

1. Use `OpenXxx` instead of `GetXxx` because the returned readers should
be correctly closed, and clarify the behaviors of the functions: they
increase the download counter
2. Use `packages-content` styles instead of `issue-content`

routers/web/user/package.go

@@ -513,9 +513,9 @@ func DownloadPackageFile(ctx *context.Context) {
 		return
 	}
 
-	s, u, _, err := packages_service.GetPackageFileStream(ctx, pf)
+	s, u, _, err := packages_service.OpenFileForDownload(ctx, pf)
 	if err != nil {
-		ctx.ServerError("GetPackageFileStream", err)
+		ctx.ServerError("OpenFileForDownload", err)
 		return
 	}