Fix(snowflake): convert VALUES with invalid expressions into UNION ALL

[georgesittas]

Snowflake doesn't support some expressions inside of the VALUES clause. For example, the following fails:

-- Invalid expression [OBJECT_CONSTRUCT('a', 'b')] in VALUES clause
SELECT * FROM (VALUES (OBJECT_CONSTRUCT('a', 'b'))) AS t(x)

Related slack thread and reference: https://docs.snowflake.com/en/sql-reference/constructs/values

Each expression must be a constant, or an expression that can be evaluated as a constant during compilation of the SQL statement. Most simple arithmetic expressions and string functions can be evaluated at compile time, but most other expressions cannot.