JSON.stringify sometimes changes values from int to float

[tomasol]

When using functions like Math.round or Math.floor, type of the attribute seems seems to be float. This is not observable when inspecting the object, but is visible using JSON.stringify.
To Reproduce
Start CLI, enter

JSON.stringify({foo:Math.round(1)})

Response: {"foo":1.0}.
Expected behavior
Expected response {"foo":1}.

Build environment:

• boa version: master (87aea64)
• OS: Ubuntu
• Version: 20.04
• Target triple: x86_64-unknown-linux-gnu
• Rustc version: 1.43.1 (8d69840ab 2020-05-04)

[HalidOdat]

This might be related to #413

[croraf]

A simpler (seems to be related) example is:

JSON.stringify(1.0)

which outputs 1.0 in Boa comparing to 1 in Chrome.

The spec leads to here for JSON.stringification of finite numbers https://tc39.es/ecma262/#sec-numeric-types-number-tostring