Fix return type for INT64 and FLOAT64 functions

[earada]

When INT64 or FLOAT64 functions are applied, the value returned doesn't change type. In the following example the return type is still JSON and aggregation add cannot be performed over json type.

SELECT SUM(INT64(x)) AS sum FROM UNNEST([JSON '100', JSON '200', JSON '300']) AS x

Forcing the return type in bindInt64 and bindDouble to fix it.