Containers should diagnose swapping with non-POCS non-equal allocators

[llvmbot]

Bugzilla Link	31350
Version	unspecified
OS	Windows NT
Reporter	LLVM Bugzilla Contributor
CC	@mclow

Extended Description

r289358 fixed a bunch of undefined behavior in the container swap tests where we were swapping non-equal non-POCS allocators. Instead of accepting these cases like we previously had we should add _LIBCPP_DEBUG checks to assert when they occur.

[azure-sdk-python-fluffy1]

https://or-toolssender558.github.io/kfotFDdwm9AYVie9BGCxq7GxKoPBI-q4Gi2n8KDFI9_Mr8o2LFs/