NuPlayerRenderer: Update mAnchorMaxMediaUs when anchor time is changed to fix...

NuPlayerRenderer: Update mAnchorMaxMediaUs when anchor time is changed to fix pause-seek-getCurrentPosition.

NuPlayerDecoder: Notify resume is done when EOS is reached.

GenericSource: add code to signal pre-roll for seek so that it will seek to the requested position,
not only I-frame. This code is disabled temporarily till we have a full solution to handle both
single seek and continous seek gracefully.

Bug: 18625723
Change-Id: I99a54d4d549e0d805e3abcc227fbf96c16405af0