When generic instance variable has a shape, it is marked movable. If it
it transitions to too complex, it needs to update references otherwise
it may have incorrect references.

That function is a bit too low level to called from multiple
places. It's always used in tandem with `rb_shape_set_too_complex`
and both have to know how the object is laid out to update the
`iv_ptr`.

So instead we can provide two higher level function:

  - `rb_obj_copy_ivs_to_hash_table` to prepare a `st_table` from an
    arbitrary oject.
  - `rb_obj_convert_to_too_complex` to assign the new `st_table`
    to the old object, and safely free the old `iv_ptr`.

Unfortunately both can't be combined into one, because `rb_obj_copy_ivar`
need `rb_obj_copy_ivs_to_hash_table` to copy from one object
to another.

It's only used to allocate the table with the right size,
but in some case we were passing `rb_shape_get_shape_by_id(SHAPE_OBJ_TOO_COMPLEX)`
which `next_iv_index` is a bit undefined.

So overall we're better to just allocate a table the size of the existing
object, it should be close enough in the vast majority of cases,
and that's already a de-optimizaton path anyway.

Right now the `rb_shape_get_next` shape caller need to
first check if there is capacity left, and if not call
`rb_shape_transition_shape_capa` before it can call `rb_shape_get_next`.

And on each of these it needs to checks if we got a TOO_COMPLEX
back.

All this logic is duplicated in the interpreter, YJIT and RJIT.

Instead we can have `rb_shape_get_next` do the capacity transition
when needed. The caller can compare the old and new shapes capacity
to know if resizing is needed. It also can check for TOO_COMPLEX
only once.

This commit changes generic ivars to respect the capacity transition in
shapes rather than growing the capacity independently.

Introduce `Module#set_temporary_name` for setting identifiers for otherwise
anonymous modules/classes.