kernel/thread: Detect in-kernel "reserved" stack overflow

Traditionally, k_thread_create() has required that the application
size the stack correctly.  Zephyr doesn't detect or return errors and
treats stack overflow as an application bug (though obviously some
architectures have runtime features to trap on overflows).

At this one spot though, it's possible for the kernel to adjust the
stack for K_THREAD_STACK_RESERVED in such a way that the arch layer's
own stack initialization overflows.  That failure can be seen by
static analysis, so we can't just sweep it under the rug as an
application failure.

Unfortunately there aren't any good options for handling it here (no
way to return failure, can't be a build assert as the size is a
runtime argument).  A panic will have to do.

Fixes: #67106
Fixes: #65584

Signed-off-by: Andy Ross <andyross@google.com>