Prevent deadlocks during VirtualDisplay creation

When creating a VirtualDisplay for a VirtualDevice, we need to do some
extra work like setting up for input injection, creating a
DisplayWindowPolicyController, and grabbing a wakelock to keep the
display awake. Some parts of this extra work end up calling back into
the DisplayManagerService from another thread, but since we're already
holding the mSyncRoot lock we sometimes get into situations where
those threads get blocked trying to acquire mSyncRoot, while holding a
lock that another thread ends up needing like the global window
manager one, so we get deadlock.

The fix in this CL is to break up the extra work the
VirtualDeviceManagerService needs to do into two parts: one part that
happens before the VirtualDisplay is created, and one part
after. Neither of these needs mSyncRoot to be held.

Fixes: 230544802
Test: atest CreateVirtualDisplayTest
Change-Id: I6a6e03f816567579510b3f1ef0705375549a3c88