vinyl: use update_def index method to update vy_lsm on ddl

When an index definition is modified by DDL in such a way that doesn't
require index rebuild (e.g. a key part type is changed from unsigned to
integer), we move the index from the old space container to the new one,
see ModifyIndex. In case of Vinyl we also need to update key definitions
and options stored in vy_lsm. We do that in swap_index space method, but
this isn't entirely correct, as this method is also called when an index
is moved without any modifications, see MoveIndex. Let's do this from
update_def index method instead, which seems to be more suitable.

The only reason this code lives in swap_index space method now is that
we didn't have update_def index method when this functionality was
introduced in the first place.