Seem UBSAN doesn't like my forced reinterpret_cast to set the Idles
Link in the Timer class. Now there are two possible solution:

  1. convert all (DECL|IMPL).*_LINK call sites to use a Timer* or
  2. split the inheritance of Idle from Timer again to maintain
     different Link<>s and move all common code into a TimerBase.

While the 1st is more correct, the 2nd has a better indicator for
Idles. This implements the first solution.

And while at it, this also converts all call sites of SetTimeoutHdl
and SetIdleHdl to SetInvokeHandler and gets rid of some local Link
objects, which are just passed to the SetInvokeHandler call.

It also introduces ClearInvokeHandler() and replaces the respective
call sites of SetInvokeHandler( Link<Timer *, void>() ).

Change-Id: I40c4167b1493997b7f136add4dad2f4ff5504b69