vector move callbacks allow mie_name instances to be stored in movable memory,
as the internal bst pointers can now be fixed during vector resize operations.
the builtin.module op behaves exactly like any other op, and is designed
to be a container for other ops of any type. it can be used as the
top-level container for other ops (other top-level containers can be used
instead).
this also changes the file format. now, an ir file can only contain a
single top-level op. any other ops in the ir must be contained
directly or indirectly by this top-level op.
this system allows dialects to register named interfaces, which are collections of function
pointers. an op can then implement this interface, providing callbacks for the interface's
virtual function pointers.
C code can request a pointer to an op's implementation of a given interface and call
virtual functions with no knowledge required about the op itself. this functonality
will also be extended to types, attributes, and dialects themselves.
any struct that contains a mie_name cannot be stored in movable memory
(i.e. any memory that may be re-allocated using realloc(), or whose
contents may be moved to a different buffer).
mie_names form part of a bst when they are added to a mie_name_map,
and moving them after this happens will result in the bst pointers
being invalidated. this causes some obscure and hard-to-debug
memory errors.
all structs that contain a mie_name (including named IR objects like
mie_register and mie_block) are no longer stored directly in vectors.
rather, vectors of pointers are used instead.
