Currently, we have NotA and NotAn, to be used dependent on whether the
following word begins with a vowel or not. To avoid this, change the
wording on NotA to be independent of this context.
https://tc39.es/ecma262/#sec-function.prototype.tostring - this is how
the spec wants us to do it. :^)
Also change the function name behaviour to only provide a name for
NativeFunctions, which matches other engines - presumably to not expose
Proxy objects, and to prevent "function bound foo() { [native code] }".