Framework: createSelector: allow 2nd arg to be array of selectors

[mcsf]

This PR allows consumers of createSelector that depend on multiple selectors to simplify their invocation of createSelector from:

createSelector(
    state => foo( state ) && bar( state ),
    state => [
        foo( state ),
        bar( state ),
        baz( state ),
    ]
);

to:

createSelector(
    state => foo( state ) && bar( state ),
    [ foo, bar, baz ]
);

To do

• Tests
• Doc block

Test live: https://calypso.live/?branch=add/create-selector-dependants-array

[mcsf]

cc @aduth for review :)

[mcsf]

I have doubts on whether the new tests are correctly described and whether they make sense, and whether it is confusing to have these two (old and new) with such similar descriptions:

✓ should accept an array of dependent state values
✓ should accept an array of dependent selectors

[lsinger]

In 5dc7d80 I have pushed a change to createSelector's README.md. Of course feel free to squash.

[aduth]

I have doubts on whether the new tests are correctly described and whether they make sense

I think they're fine. Potentially they could be collapsed into a single test, testing both that the memoization works as intended, and that the individual selectors in the getDependants array get called with the arguments. Not sure it's a big deal enough to change.

I tweaked a few things in f25e3b5. If looks alright to you, I'm fine with merging this 👍

[mcsf]

Awesome, thanks for your help, @lsinger and @aduth. I'll squash and merge!