Revert "PIE: slight style change"

This reverts commit 601b5c2d44c0aca63dcaa089677cf12a3b40ff77.
Fix incorrect fragment animation used for hiding fragments
Mirror of support lib patch
https://android-review.googlesource.com/#/c/60032/ into
frameworks/base.

AOSP Commit: https://android-review.googlesource.com/#/c/60167/
HALO: Option to pause the underlying app (1/2)

- adds an option to pause the active app when using HALO
- this is enabled by default for devices with low memory
- (currently: <640MB RAM available to the kernel)
Reworked transparent layer
When a halo'ed window is opened, the transparent layer will be always visible. It will manage the background dim.
This fixes some apps dimming its sandboxed processes (like chrome).

LayerActivity manages its own lifecycle. When it's focused after paused it finishes itself.

System processes (identified by "android" pkg in SystemUI and system uid in Activity) don't use the layer and still use their own background. This
has been kept this way to not interfere with their activity.
Check themes of current user, not user 0.
Fix systemUI
Signed-off-by: igio90 <giovanni.rocca.90@gmail.com>