fix(expect): expect.toEqual need to return original obj

[eryue0220]

If support addEqualityTester, this case will fail, because it return a new object.

import { expect } from "https://deno.land/std/expect/mod.ts";

class Volume { /* specify logic*/ }

function createVolume() {
  return new Volume();
}

function areVolumeEqual(a: unknown, b unknown) {
   return a instacneof Volume && b instanceof Volume
}

Deno.test('custom equality tester', () => {
    expect.addEqualityTester([areVolumeEqual]);
    const volume1 = createVolume();
    const volume2 = createVolume();
    expect(volume1).toEqual(volume2);
});

And current expect(source1).toEqual(source2) will return false.

[CLAassistant]

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[kt3k]

This modifies the input object. That doesn't look a good idea.

[eryue0220]

This modifies the input object. That doesn't look a good idea.

Yeah, I'll consider other solutions.

[eryue0220]

If the #4246 is merged, this pr will be solved as well. And it's no need any more.