vinyl: fix crash on extending secondary key parts with primary

If a secondary index is altered in such a way that its key parts are
extended with the primary key parts, rebuild isn't required because
`cmp_def` doesn't change, see `vinyl_index_def_change_requires_rebuild`.
In this case `vinyl_index_update_def` will try to update `key_def` and
`cmp_def` in-place with `key_def_copy`. This will lead to a crash
because the number of parts in the new `key_def` is greater.

We can't use `key_def_dup` instead of `key_def_copy` there because
there may be read iterators using the old `key_def` by pointer so
there's no other option but to force rebuild in this case.

The bug was introduced in commit 64817066 ("vinyl: use update_def
index method to update vy_lsm on ddl").

Closes #10095

NO_DOC=bug fix