Reimplement isEqual without pulling in massive lodash.isequal.

[benjamn]

Follow-up to #4915. I have kept the tests from that PR, just not the lodash-based implementation of isEqual.

The lodash.isequal package has a ton of extra features we don't need, and weighs in at a whopping 10KB minified (3.8KB after gzip). Very little of that machinery is really necessary to fix #4824.

I extracted this functionality into a separate npm package called @wry/equality, so we have the flexibility to depend on the same logic in other packages without importing apollo-utilities.

Here's the new implementation.

[benjamn]

I was mistaken when I claimed, "Since the lodash.isequal package is already used by react-apollo, this change is likely to decrease total bundle size," because React Apollo will soon be removing lodash.isequal: apollographql/react-apollo@feb9b0c

[benjamn]

@capaj In the process of reimplementing isEqual I did find a bug in lodash.isequal, which I thought you might find interesting because you advocated for not testing the lodash.isequal implementation:

const isEqual = require("lodash.isequal");

const a = { self: { self: { self: {}}}};
a.self.self.self.self = a;

const b = { self: {}};
b.self.self = b;

console.log(isEqual(a, b)); // true
console.log(isEqual(b, a)); // false

It would be fine for isEqual to return false in both cases, but returning different results when the arguments are reversed violates symmetry (one of the required properties of any equivalence relation).

[capaj]

Very nice find. Did you open a bug in Lodash repo?

[benjamn]

@capaj Planning to do that, though I think we'll stick with the smaller implementation. Thanks for sending me down this path!

[hwillson]

Great @benjamn!! 👍