Update display density of Task thumbnails

This is to fix an issue caused by Bitmap.sDefaultDensity being
updated when configuration changes. Creating a Bitmap with Bitmap.wrapHardwareBuffer
then uses this default value which may not have been set using the correct
display density.

Flag: EXEMPT bugfix
Test: locally tested on comet
Bug: 421205443

Change-Id: I3b63e6306fce1b5c7d3b7aca29df660b73b8d558