Support ALTER COLUMN RESTART WITH

As a replacement for the broken `sys.alter_seq_restart` stored procedure. For general, non-identity sequence changes we'll probably just want to implement ALTER SEQUENCE.

Also remove support for SET INCREMENT BY because it didn't actually work and not straight forward to do.
Are you allowed to restart with a value less than the previous max? e.g. 
```
ALTER TABEL t ALTER COLUMN id RESTART WITH 80
```