Avoid exotic objects (e.g. named/indexed getters/setters)

[domenic]

I just wrote up https://code.google.com/p/chromium/issues/detail?id=503971#c6 and it'd probably be worth capturing here.

[annevk]

See https://www.w3.org/Bugs/Public/show_bug.cgi?id=26986 which would make this more clearly a stupid idea from an IDL perspective.

[dbaron]

@travisleithead points out that exotic object is defined in ECMA-262.

[torgo]

Reference an ecmascript definition. https://ecma-international.org/ecma-262/6.0/#sec-exotic-object

[torgo]

Something should go in section 2.

[domenic]

In IDL we have since renamed the objects so-defined "legacy platform objects"

Also, please use https://tc39.github.io/ecma262/.