Import AndroidX from build 6848439

  ./update_prebuilts.py -x 6848439

Import AndroidX heifwriter only from build 6848439 in order to
pick up a fix for b/168660257.

A full update is currently blocked by b/170339873.

bug: 168660257

Change-Id: Ibfe07237c4a0dca937dacf186c6618d7fb439fb1
15 files changed