Clean up fastAddProperties and make it more correct

[dmytrorykun]

Summary

This PR makes some fixes to the fastAddProperties function:

• Use if (!attributeConfig) instead of if (attributeConfig === undefined) to account for null.
• If a prop has an Object attributeConfig with a diff function defined on it, treat it as an atomic value to keep the semantics of diffProperties.

How did you test this change?

Build and run RNTester app.

[react-sizebot]

Comparing: 7039834...fbcbb40

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.66 kB	6.66 kB	=	1.82 kB	1.82 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	494.06 kB	494.06 kB	=	88.22 kB	88.22 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.67 kB	6.67 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	498.86 kB	498.86 kB	=	88.93 kB	88.93 kB
facebook-www/ReactDOM-prod.classic.js	=	591.22 kB	591.22 kB	=	103.96 kB	103.96 kB
facebook-www/ReactDOM-prod.modern.js	=	567.44 kB	567.44 kB	=	100.36 kB	100.36 kB
test_utils/ReactAllWarnings.js	Deleted	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Generated by 🚫 dangerJS against fbcbb40

[javache]

What I was just mentioning about: we could change the default here and stop ignoring any properties that do not have validAttributes entry.

[yungsters]

That requires the new parser, no? Otherwise, we might get a native exception.

[rickhanlonii]

Update native to ignore unknown props?

This would take us a step closer to removing Static View Configs. We would need this, and a way to specify the bubbling behavior of events. Or we could convert all custom events to be direct, and store a config for which built-in events should bubble (which would also fix the bubbing/direct event name collision bug).

[dmytrorykun]

Update native to ignore unknown props?
This would take us a step closer to removing Static View Configs.

That is already planned!

[yungsters]

Consider unit tests, since this logic seems quite nuanced. It's be a good way to also compare the old and new code paths against each other.

[yungsters]

I personally prefer the explicitness of attributeConfig == null (which checks for both undefined and null), but this works, too.

[yungsters]

Consider leaving an explanatory comment here.

[javache]

Could this work?

    let newValue = typeof nextProp === 'function' ? true : nextProp;
    if (typeof attributeConfig === 'object' && typeof attributeConfig.process === 'function') {
      newValue = attributeConfig.process(nextProp);
    }

[yungsters]

Could do typeof attributeConfig?.process === 'function', too.