Add support for user-defined table types (#52)

Simple extension of the grammar to support #51 

The official documentation of the structure is
[here](https://learn.microsoft.com/en-us/sql/t-sql/statements/create-type-transact-sql?view=sql-server-ver16)

First commit is the manual changes, second commit is the autogenerated
code (to ease reviewing).

Author: EnchoMishinevQC