Function to_jsonb 

pub fn to_jsonb(
    ecx: &ExprContext<'_>,
    expr: HirScalarExpr,
) -> Result<HirScalarExpr, PlanError>

Converts an expression to SqlScalarType::Jsonb.

The rules are as follows:

• SqlScalarType::Booleans become JSON booleans.
• All numeric types are converted to Float64s, then become JSON numbers.
• Records are converted to a JSON object where the record’s field names are the keys of the object, and the record’s fields are recursively converted to JSON by to_jsonb.
• Other types are converted to strings by their usual cast function and become JSON strings. That cast can fail (see to_string), in which case we propagate the planning error instead of panicking.