It was possible to create virtual columns with incompatible
GENERATED ALWAYS expression data types:

  CREATE TABLE t1 (a INT, b POINT GENERATED ALWAYS AS (a));
  CREATE TABLE t1 (a POINT, b INT GENERATED ALWAYS AS (a));

These data type combinations are not allowed in other cases,
e.g. INSERT, UPDATE, SP variable assignment.

Fix:

Disallowing bad combinations of the column data type and its
GENERATED ALWAYS expression data type.