feat(optimizer)!: annotate type for Snowflake EXP function

[fivetran-BradfordPaskewitz]

Documentation: https://docs.snowflake.com/en/sql-reference/functions/exp

Platform Support:
Platform | Supported | Arguments | Return Type | Notes
Snowflake | Yes | Numeric | Numeric (float) | Native EXP function
BigQuery | Yes | Numeric convertible | FLOAT64 | Native EXP function
Redshift | Yes | Integer, Decimal, Double | DOUBLE PRECISION | Native EXP function
PostgreSQL | Yes | Numeric | DOUBLE PRECISION | Native EXP function
Databricks | Yes | Numeric | DOUBLE | Native EXP function
DuckDB | Yes | Numeric | Numeric (double) | Native EXP function
TSQL | Yes | Float expression | Float | Native EXP function

[geooo109]

We can remove the validate_identity tests. For all the dialects the function is the same, and we cover it in the identity.sql file.

[geooo109]

Let's make this DOUBLE.