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/Constants.cs

@@ -224,6 +224,9 @@ namespace GitHub.Runner.Common
             public static class Agent
             {
                 public static readonly string ToolsDirectory = "agent.ToolsDirectory";
+
+                // Set this env var to force a node version for internal functions (e.g hashfiles). This does NOT affect the version of node actions.
+                public static readonly string ForcedNodeVersion = "GITHUB_ACTIONS_RUNNER_FORCED_NODE_VERSION"; 
             }
 
             public static class System