Don't send config change when display is removed

When a private display is removed, we're finishing all activities
that were on that display. But because the display will not be
available during activity finish process, we're fist moving all
stacks to the back of the default display, so that the removed
display won't be referenced accidentally.
This, however, can cause an additional resize message to the client
from the WindowManager if the size of the default display is
different, which will cause a configuration change. To avoid that
this CL freezes the config of the stacks being finished by overriding
to their current configs.

Bug: 73379938
Test: ActivityManagerMultiDisplayTests#testContentDestroyOnDisplayRemoved
Change-Id: I20e0becab097075ccb84e471e366a2ace37ab7cc