Improved encoding of NSNumber in OpenAPIValueContainer

[czechboy0]

Motivation

When getting CoreFoundation/Foundation types, especially numbers, they automatically bridge to Swift types like Bool, Int, etc. That casting is pretty flexible, and allows e.g. casting a number into a boolean, which isn't desired when encoding into JSON, as false and 0 represent very different values.

Previously, we relied on the automatic casting to know how to encode values, however that produced incorrect results in some cases.

Modifications

Add explicit handling of CF/NS types and try to encode using that new method before falling back to testing for native Swift types. This ensures that the original intention of the creator of the CF/NS types doesn't get lost in encoding.

Result

Correct encoding into JSON of types produced in the CF/NS world, like JSONSerialization.

Test Plan

Added unit tests.

[simonjbeaumont]

Well... this is fun. Nice patch though.