Sharesheet - Load images off main thread

To prevent main thread from being blocked and potential ANRs, load
images on AsyncTasks. If no images are successfully loaded within a
timeout period, hide the content preview area. Optimize scrolling by
reusing the views in their entirety and not reloading images. Also
allow for more time for direct share loading

Bug: 132698784
Test: Manual
Change-Id: Ia73e9b6912bf36a1c6c9660423d6f0602e832187