Fire useEffect in reverse component depth order

[developit]

This changes the ordering of useEffect callbacks so that they fire roughlydeterministically in order of reverse tree depth (innermost to outermost). Callbacks will still fire in-order for multiple useEffect()'s within a single component, but the callbacks for a child component will always fire before those of a parent.

We already invoked useEffect() callbacks in reverse-depth-order for normal/full tree updates, since they were pushed into the queue from options.diffed() which fires inner-to-outer. With this PR, that ordering of useEffect callbacks is now also used when a parent subtree and child subtree are both enqueued for rendering, and the parent update does not descend to the child/grandchild (due to sCU/memo). In that case, we always render the parent component/tree before the child, but will now fire the child's useEffect callbacks before those of the parent.

h/t @wonderful-panda for uncovering this: https://twitter.com/wonderful_panda/status/1467015985672892416

We don't have specific timing that we state these calls will adhere to, so it seems like aligning with React makes the most sense here. React fires in-order within a component, but inner-to-outer between components (demo):

[github-actions]

Size Change: +70 B (0%)

Total Size: 42.2 kB

Filename	Size	Change
hooks/dist/hooks.js	1.17 kB	+23 B (1%)
hooks/dist/hooks.module.js	1.18 kB	+25 B (2%)
hooks/dist/hooks.umd.js	1.24 kB	+22 B (1%)

ℹ️ View Unchanged

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test-utils/dist/testUtils.umd.js	515 B	0 B

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[JoviDeCroock]

@developit I think we're already executing in the right order https://codesandbox.io/s/snowy-wave-jfz5s?file=/src/index.js

[developit]

@JoviDeCroock ah, I think I see why - we push into the afterPaintCallback queue from within options.diffed, which is called inner-to-outer. Good catch.

[developit]

Ah - figured it out: this affects updates when components are memoized or bail out via sCU.
In this modified version of the demo, triggering an update of Inner + Outer in the same batch will fire the outer callback before the inner one:
https://codesandbox.io/s/wizardly-tdd-qwz16?file=/src/index.js

I believe this is why only two tests are red from the change - we were already calling inner-to-outer in the majority of cases, this only affects the case where (state-based) updates are scheduled for both a subtree and its (grand)parent.

[developit]

#3356 (review)

[coveralls]

Coverage increased (+0.001%) to 99.627% when pulling a496224 on useeffect-reverse-depth-ordering into 70bc35a on master.