Fix interface.functions fragment name conflict with Object prototype keys

[predetermined]

Fixes #2054

[ricmoo]

Unfortunately Map is not in older ES3 environments and so it isn’t a candidate for v5. :s

In v6, more modern JavaScript features are being used though, so it will be added then. :)

[predetermined]

@ricmoo Oh, I haven't thought about this. What do you think about using Object.create(null)?

Reference: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/create#custom_and_null_objects

[ricmoo]

Hmmm, that seems scary and I don’t fully understand all the consequences of this, especially in more obscure environments. :s

…can behave in unexpected ways.

also doesn’t inspire me with confidence. :p

I think for v5, I won’t change this and just require fully-qualified signatures (e.g. "prototype()"). In v6 a lot of these things will be operating via Proxy as well, so this is an important test case to remind myself of.