Add useLazyRef hook

[AndrewMusgrave]

WHY are these changes introduced?

@beefchimi and I added this while working on #2105, I broke this out of the other PR so we can take our time working on 2105 and use this hook in the meantime.

It'll allow for lazy initialization of refs, see jsdocs for a little more information

WHAT is this pull request doing?

• Adding hook + jsdoc
• Adding tests

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide
• For visual design changes, pinged one of @ HYPD, @ mirualves, @ sarahill, or @ ry5n to update the Polaris UI kit

[BPScott]

Looks solid.

I note that quilt has a react-hooks package that contains a similar implementation: https://github.com/Shopify/quilt/blob/master/packages/react-hooks/src/hooks/lazy-ref.ts

At some point in the future if we end up adding lots of these general-purpose hooks it might be worth thinking about pushing them into quilt. I can see useIsAfterIntitalMount being a useful one all over the place.

[beefchimi]

it is remarkable how this is almost identical to the quilt version Ben pointed out

[AndrewMusgrave]

Looks solid.

I note that quilt has a react-hooks package that contains a similar implementation: https://github.com/Shopify/quilt/blob/master/packages/react-hooks/src/hooks/lazy-ref.ts

At some point in the future if we end up adding lots of these general-purpose hooks it might be > worth thinking about pushing them into quilt. I can see useIsAfterIntitalMount being a useful one > all over the place.

It looks like they have a similar use mounted hook as well. It might be beneficial to share our code so we don't duplicate it. Other libraries like online store ui could make use of them as well, what do you think @beefchimi

[beefchimi]

@AndrewMusgrave definitely in favour of sharing more hooks!

[BPScott]

It looks like they have a similar use mounted hook as well.

Their hook has cleanup so it toggles if the current component is mounted or not, while I believe yours would set a value after initial mount then never change so they're similar but subtly different

[AndrewMusgrave]

Yup the two mounting hooks are fundamentally different, with different uses. However I added a similar one here, they're almost identically however the quilt version doesn't initialize a false value, which might be an error.