Add ALLOW_SLIPPERY_TOUCHES to make StatusBarTouchController slippery

LauncherActivity uses FLAG_SLIPPERY for certain interactions. For
example, when home screen is shown, and the user pulls down from not the
top of the screen, and notification shade is getting displayed, then the
touch should be getting transferred to the NotificationShade using
FLAG_SLIPPERY.

The newly introduced permission is added to launcher in order for this
flag to be applied to the window.

Bug: 206188649
Bug: 157929241
Test: reviewed logs, ensure that NexusLauncherActivity has FLAG_SLIPPERY
Test: re-ran the performance regression test
Merged-In: I8d05fa3663687b5382a59b0d47cdac404844c3b7
Change-Id: I8d05fa3663687b5382a59b0d47cdac404844c3b7
(cherry picked from commit 918776ee)
Merged-In:I8d05fa3663687b5382a59b0d47cdac404844c3b7