Defer adapter updates while RV is computing layout

Bug: 29149374

It appears that the ItemAnimator#isRunning callback can happen at times
when RV is computing its layout and hence adapter updates are not
allowed. We now defer adapter updates using a handler in this case and
also take care to preserve the ordering of updates.

Change-Id: I8ef243f5a689755dc2ab665471610e0501c72bcc