Adds all_apps_blur flag.

This enables blur both for Taskbar and Launcher, but in slightly
different ways.

For Taskbar All Apps, we apply blur to the overlay window, and
for Launcher All Apps, we utilize the existing DepthController to
blur the wallpaper window. For similicity, we currently fade out
workspace/hotseat to avoid awkward view + window blurs which
don't look that good. This is not the POR, but I think it achieves
most of the effect and will help us get some blur exposure.

Separately I will continue to investigate options such as blurring
workspace in a clever way so it feels blended with the wallpaper,
reusing the Taskbar window and connecting it to LauncherState, or
using a SurfaceView (though I spent quite some time trying this and
it seemed the same as the original issue).

In both cases, we use a 20-30% opacity scrim with a set color, and a
panel that blends 40% opacity of a dark/light color with 10% white.

Also updated some incorrect isTablet checks which really should have
been checking shouldShowAllAppsOnSheet(), which includes the
all_apps_sheet_for_handheld flag.

Demo: https://drive.google.com/file/d/1Ov9Dg3R9YHNfisfxNf97ZIhlDeEA1IWj/view?usp=sharing&resourcekey=0-l_SDpqpS4HtOb10a3b_jNg

Other upcoming improvements: interpolator tweaks, colors of things
inside the app panel (tabs, private space, search results, etc).

Bug: 400827727
Bug: 371343636
Test: Manual
Flag: com.android.launcher3.all_apps_blur
Change-Id: Ic7063cd822f39a5977715b5477f825bf11e57bdf