EventHub: Re-open Devices serially when AssociatedDevice changes

This CL changes behavior so that when an AssociatedDevice changes,
all affected Devices will be re-opened serially, where the
DEVICE_REMOVED notification of one device closing is followed by the
DEVICE_ADDED signal of its new counterpart, before proceeding with the
re-opening of the next affected Device.

This is to temorarily curb the side-effects of delayed AssociatedDevice
changes by reducing the number of cases where we send device removed
notifications immediately after an input device is first connected,
followed by the addition of a new InputDevice. These kind of "hotplug"
events are detrimental to many tests and may have side effects in
production.

This CL relies on some assumptions on how devices will be merged in
InputReader, so it does not solve the problem for all cases. It only
aims to reduce the likelihood of impact temporarily until
AssociatedDevice changes can be processed separately in InputReader,
which is backlogged as b/281822656.

Bug: 397208968
Test: Presubmit
Flag: EXEMPT bug fix
Change-Id: I61818076a720a5474de8cbeb431ddbceec6e1545