timers: improve setTimeout/Interval performance

This commit improves timers performance by making functions
inlineable and avoiding the creation of extra closures/functions.

This commit also makes setTimeout/Interval argument handling
consistent with that of setImmediate.

These changes give ~22% improvement in the existing 'breadth' timers
benchmark.

PR-URL: https://github.com/nodejs/node/pull/8661


Reviewed-By: Franziska Hinkelmann <franziska.hinkelmann@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>