DMN16 — number(from) function does not accept number as input

Currently, `string(string_variable) = string_variable`, but `number(number_variable) = null`.
This leads to surprising results like `number(5) = null` but `number("5") = 5`.
Let's add a function `number(from)` which would accept `number` as the parameter.

Add number(from: number)

Add a version of the number(from) function that accepts a number as an input and returns it, which is in line with the behavior of other conversion functions, e.g. string(from), and helps in situations where expressions produce, e.g. a string or a number.