Implement native function of nanvl(87)

[guixiaowen]

Description

Convert Spark's built-in function nanvl to execute as a native function.

Spark function name:
nanvl

Method description:

nanvl(expr1, expr2) - Returns expr1 if it's not NaN, or expr2 otherwise.

Examples:

SELECT nanvl(cast('NaN' as double), 123);
123.0

To Native function

f::math::nanvl