Fix!(spark): parse computed column constraints appropriately

[georgesittas]

Fixes #2301

References:

• https://docs.databricks.com/en/sql/language-manual/sql-ref-syntax-ddl-create-table-using.html
• https://learn.microsoft.com/en-us/sql/t-sql/statements/create-table-transact-sql?view=sql-server-ver16
• https://learn.microsoft.com/en-us/sql/relational-databases/tables/specify-computed-columns-in-a-table?view=sql-server-ver16
• https://learn.microsoft.com/en-us/sql/t-sql/functions/cast-and-convert-transact-sql?view=sql-server-ver16
• [SPARK-41290][SQL] Support GENERATED ALWAYS AS expressions for columns in create/replace table statements apache/spark#38823