timers: fix processing of nested timers

Whenever a timer is scheduled within another timer, there are a few
known issues that we are fixing:

* Whenever the timer being scheduled has the same timeout value as the
outer timer, the newly created timer can fire on the same tick of the
event loop instead of during the next tick of the event loop
* Whenever a timer is added in another timer's callback, its underlying
timer handle will be started with a timeout that is actually incorrect

This commit consists of
https://github.com/nodejs/node-v0.x-archive/pull/17203 and
https://github.com/nodejs/node-v0.x-archive/pull/25763.

Fixes: https://github.com/nodejs/node-v0.x-archive/issues/9333
Fixes: https://github.com/nodejs/node-v0.x-archive/issues/15447
Fixes: https://github.com/nodejs/node-v0.x-archive/issues/25607
Fixes: https://github.com/nodejs/node/issues/5426
PR-URL: https://github.com/nodejs/node/pull/3063