use Object.is for checking mutated children

[just-boris]

fixes #7424

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[chicoxyzzy]

If we're going to use object-is package we also should use it here IMO. cc @zpao

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[just-boris]

вы тут ночуете что ли?

Of course, I'd like to found all other usages and replace with this lib as well, like it happens with object-assign now.
But let's wait for feedback from team members first.

[caub]

except NaN, is there another case where it's useful?

[just-boris]

This also doesn't differ +0 and -0, but I don't think that this can be useful for mutation check.

[zpao]

Using this external module is going to be more trouble than it's worth right now. We'd have to do something like #6376.

Could you instead inline a copy of the fn like we did in #6132. It's a couple extra bytes but not a huge deal.

[caub]

Can't this be a polyfill since Object.is is now in browsers/node.js?

[zpao]

We can discuss that separately. Right now we haven't required the polyfill exist in the other places it's used so we won't start now.

[just-boris]

I think this is not actual, because #7455 removes this code at all.

Also, now Object.is is used only in ReactPropTypes.js module, so there is no need to create it as shared module.