No longer embedding activity if started-for-result across TFs

Instead of sending RESULT_CANCELED to the caller activity, let's
making sure the caller activity can get the result by stop embedding
the result activity in another TaskFragment.

Bug: 236668365
Test: atest TaskFragmentTest
Change-Id: I2a1d3203cc64df6a3b2004529d067990ae17d1d5
3 files changed