Substring function does not support CHAR type

[ebyhr]

While substr function accepts char type, substring function doesn't.

SELECT substr(cast('abcd1234' as char(8)), 1, 4);
→ OK

SELECT substring(cast('abcd1234' as char(8)), 1, 4);
→ Unexpected parameters (char(8), integer, integer) for function substring. Expected: substring(varchar(x), bigint, bigint) , substring(varchar(x), bigint)

https://prestosql.io/docs/current/functions/teradata.html

[findepi]

substring is part of teradata functions
(when we have function namespaces, this will be more clear to users as well).

@ebyhr did you check that substring in teradata works with char values too?

[findepi]

Requires #3456 being resolved first.

[ebyhr]

Yes, I checked it before filing the issue.