mm/slub, kunit: add a KUnit test for SLUB debugging functionality

SLUB has resiliency_test() function which is hidden behind #ifdef
SLUB_RESILIENCY_TEST that is not part of Kconfig, so nobody runs it.
KUnit should be a proper replacement for it.

Try changing byte in redzone after allocation and changing pointer to next
free node, first byte, 50th byte and redzone byte.  Check if validation
finds errors.

There are several differences from the original resiliency test: Tests
create own caches with known state instead of corrupting shared kmalloc
caches.

The corruption of freepointer uses correct offset, the original resiliency
test got broken with freepointer changes.

Scratch changing random byte test, because it does not have meaning in
this form where we need deterministic results.

Add new option CONFIG_SLUB_KUNIT_TEST in Kconfig.  Tests next_pointer,
first_word and clobber_50th_byte do not run with KASAN option on.  Because
the test deliberately modifies non-allocated objects.

Use kunit_resource to...