This allows these methods to be called from ractors.

Add new exported function `rb_vm_lock_with_barrier()` that requires
users to include "vm_sync.h"

allocation_info_tracer_compact_update_object_table_i deletes entries where
the key is no longer in the GC heap but did not free the allocation_info
causing the memory to be leaked.

The embed layout is way more common than the heap one,
especially since WVA.

I think it makes for more readable code to inverse the
flag.

`RSHAPE_PARENT` is error prone because it returns a raw untagged
shape_id.

To check if a shape is a direct parent of another, tags should be
discarded. So providing a comparison function is better than exposing
untagged ids.

It has been marked as obsolete for a while and I see no reason
to keep it.