Update TimerFileDescriptor to support different task types

Introduced ITask and its concrete implementations (e.g.
MessageTask, RunnableTask) for TimerFileDescriptor to enable more
flexible task scheduling.

Bug: 366373064
Test: atest NetworkStaticLibTests
Change-Id: I3a5177b66916f50f3f943d8b63b0c760bece60e4
2 files changed