Scale bitmap shaders for target density

Also fixes progress bar sample tile to reflect density and ensures
that ProgressBar.tileify() clones inner drawables into the correct
density.

Bug: 31841123
Test: BitmapDrawableTest#testPreloadDensity()
Test: ThemeHostTest
Test: Visual inspection of ApiDemos
Change-Id: I9dcb9817d8d91d61ff0215987247e9e7fb089c46