process: make this value consistent

The value of `this` for callbacks of `nextTick()` can vary depending on
the number of arguments. Make it consistent.

PR-URL: https://github.com/nodejs/node/pull/14645
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>

lib/internal/process/next_tick.js

@@ -141,7 +141,7 @@ function setupNextTick() {
           callback(args[0], args[1], args[2]);
           break;
         default:
-          callback.apply(null, args);
+          callback(...args);
       }
     }
   }

test/parallel/test-next-tick.js

@@ -51,7 +51,7 @@ process.nextTick((a, b) => {
 }, 42, obj);
 
 process.nextTick(function() {
-  assert.strictEqual(this, null);
+  assert.strictEqual(this, undefined);
 }, 1, 2, 3, 4);
 
 process.nextTick(() => {