fix: prevent name collisions when launching multiple node-based servers on same node_modules

Before this change: if two (or more) node-based servers have been
started on the same node_modules dir, the could override each others
temporary port files, resulting in some of the servers not correctly
launching.
With this change: each server process makes sure to write distinct
temporary and final files for transporting selected port number to the
launching java process.
This is a fixup for #2462.

Refs: #2462, #2542

Author: simschla

lib/src/main/resources/com/diffplug/spotless/npm/common-serve.js

@@ -35,12 +35,14 @@ function getInstanceId() {
 
 var listener = app.listen(0, "127.0.0.1", () => {
 	const instanceId = getInstanceId();
+	const tempFileName = `server-${instanceId}.port.tmp`;
+	const finalFileName = `server-${instanceId}.port`;
 	debugLog("Server running on port " + listener.address().port + " for instance " + instanceId);
-	fs.writeFile("server.port.tmp", "" + listener.address().port, function (err) {
+	fs.writeFile(tempFileName, "" + listener.address().port, function (err) {
 		if (err) {
 			return console.log(err);
 		} else {
-			fs.rename("server.port.tmp", `server-${instanceId}.port`, function (err) {
+			fs.rename(tempFileName, finalFileName, function (err) {
 				if (err) {
 					return console.log(err);
 				}