[YCQL] CAST to TINYINT is not supported

[OlegLoginov]

Jira Link: DB-4700

> CREATE TABLE k.num (pk int PRIMARY KEY, i16 smallint);
> INSERT INTO k.num(pk, i16) VALUES (0, 1000);
> SELECT CAST(i16 as TINYINT) FROM k.num;

InvalidRequest: Error from server: code=2200 [Invalid query] message="Invalid Function Call. Failed calling 'cql_cast(smallint)'. Signature mismatch in call to builtin function 'cql_cast'
SELECT CAST(i16 as TINYINT) FROM k.num;
       ^^^^
 (error -214)"