In `FakeAsyncZoneSpec`, there are several variables and APIs to identify
different times, and the names are confusing, in this commit, they are
renamed for more clear understandings.
1. currentTickTime, the tick millis advanced.
2. getFakeBaseSystemTime(), return the fake base system time.
3. setFakeBaseSystemTime(), set the fake base system time.
4. getRealSystemTime(), get the underlying native system time.
PR Close#39127
c53f19ac47