Prefer node16 over node12 when running internal scripts (#1621)

* Use 16 to run RunnerService.js

* Execute hashfiles using node16

* Run downloadCert.js using node16

* Run makeWebRequest.js using node16

* Run macos-run-invoker.js using node16

* Run hashFiles.js using node16

* Update tests to use node16

* Update documentation to recommend node16

* Duplicate macos service js fix for 16

* Add PR link

* Revert ADR node change

* Merge node12/16 retainment IFs

* Try both node12 and node16

* Close if

* Revert "Update tests to use node16"

This reverts commit bbca7b9f1c.

* Fix condition

* Unfurl if condition

* Allow user to force a node version

* Format update template

* Comment env var

* Rename vars

* Fix naming

* Fix rename

* Set node ver override if job message has it

* Format executionContext

* Can only receive 'forceNode12' or nothing from FF
No specific node version from server

Co-authored-by: Ferenc Hammerl <hammerl.ferenc@gmail.com>

src/Runner.Common/Util/NodeUtil.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.ObjectModel;
+
+namespace GitHub.Runner.Common.Util
+{
+    public static class NodeUtil
+    {
+        private const string _defaultNodeVersion = "node16";
+        public static readonly ReadOnlyCollection<string> BuiltInNodeVersions = new(new[] {"node12", "node16"});
+        public static string GetNodeVersion()
+        {
+            var forcedNodeVersion = Environment.GetEnvironmentVariable(Constants.Variables.Agent.ForcedNodeVersion);
+            return !string.IsNullOrEmpty(forcedNodeVersion) && BuiltInNodeVersions.Contains(forcedNodeVersion) ? forcedNodeVersion : _defaultNodeVersion;
+        }
+    }
+}