feat(optimizer)!: Add function and annotate snowflake HEX DECODE STRING and BINARY functions

[fivetran-amrutabhimsenayachit]

Add function and annotate snowflake HEX DECODE STRING and BINARY functions

Documentation:

https://docs.snowflake.com/en/sql-reference/functions/hex_decode_binary
https://docs.snowflake.com/en/sql-reference/functions/hex_decode_string

[fivetran-amrutabhimsenayachit]

HEX_DECODE_BINARY is already handled and has a func class - UnHex.

**Cross-Dialect Transpilation:**
Snowflake: HEX_DECODE_BINARY("48656C6C6F")
BigQuery: FROM_HEX(\48656C6C6F\)
DuckDB: UNHEX("48656C6C6F")
PostgreSQL: UNHEX("48656C6C6F")

Following tests already exist:

self.validate_all(
            "SELECT HEX_DECODE_BINARY('65')",
            write={
                "bigquery": "SELECT FROM_HEX('65')",
                "duckdb": "SELECT UNHEX('65')",
                "snowflake": "SELECT HEX_DECODE_BINARY('65')",
            },
        )