This fixes a rebase issue between the int_dict introduction and use
for people.js with the introduce of filter_values on dict.js and use
inside people.js.
We have ~5 years of proof that we'll probably never
extend Dict with more options.
Breaking the classes into makes both a little faster
(no options to check), and we remove some options
in FoldDict that are never used (from/from_array).
A possible next step is to fine-tune the Dict to use
Map internally.
Note that the TypeScript types for FoldDict are now
more specific (requiring string keys). Of course,
this isn't really enforced until we convert other
modules to TS.
The delete operator could throw a TypeError when attempting to
remove a non-configurable property, which is rare in practice since
they can only be created using `Object.defineProperty()` and
`Object.freeze()`. We also never uses the output of `del()` anyway.
Anders Kaseorg
Tim Abbott
Steve Howell
Thomas Ip