samples, tests: Add z_libc_partition to all test domains

When a memory domain is initialized, the z_libc_partition must be
included so that critical libc-related data can be accessed.

On ARM processors without TPIDRURO when THREAD_LOCAL_STORAGE is enabled,
this includes the TLS base pointer, which is used for several
thread-local variables in the kernel.

Signed-off-by: Keith Packard <keithp@keithp.com>