alter: require rebuild of all secondary vinyl indexes if pk changes

If the primary key is modified, we schedule rebuild of all non-unique
(including nullable) secondary TREE indexes. This is valid for memtx,
but is not quite right for vinyl. For vinyl we have to rebuild all
secondary indexes, because they are all non-clustered (i.e. point to
tuples via primary key parts). This doesn't result in any bugs for now,
because rebuild of vinyl indexes is not supported, but hopefully this is
going to change soon. So let's introduce a new virtual index method,
index_vtab::depends_on_pk, which returns true iff the index needs to be
updated if the primary key changes, and define this new method for vinyl
and memtx TREE indexes.