feat: Add Modal deprecation warnings (non-breaking deprecation)

[brandonlenz]

Summary

Adds deprecation warnings to Modal components and functions/hooks in preparation for official removal from this library

Related Issues or PRs

closes #786

(I'm now realizing this issue was still under "Needs Requirements". I figured it'd be some low-hanging-fruit to get a warning out to consumers of this library as early as possible. Whenever we're ready, this branch exists to be merged (or updated then merged) pending any requirement changes)

How To Test

> git fetch
> git checkout bl-modal-deprecation-warning-786

> yarn storybook

Then preview any Modal story and take note of the console warnings (screenshots below as well)

Screenshots (optional)

Any single export will show a deprecation warning as follows:

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Multiple exports will each show specific deprecation warnings

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[trussworks-infra-zz]

	Warnings
⚠️	This PR does not include changes to storybook, even though it affects component code.

Generated by 🚫 dangerJS against 3b7b689

[suzubara]

this looks great! do you mind updating the Modal tests to expect this warning? There are some examples of testing the deprecation warning in other components that use it, like NavList

[brandonlenz]

this looks great! do you mind updating the Modal tests to expect this warning? There are some examples of testing the deprecation warning in other components that use it, like NavList

@suzubara good call. Thanks for pointing those out! d6194d3

[suzubara]

awesome, thank you!

[suzubara]

the Happo report for the last commit has some weird diffs, like icons/fonts not showing up.. it might be worth trying to re-run to see if they were spurious

[brandonlenz]

the Happo report for the last commit has some weird diffs, like icons/fonts not showing up.. it might be worth trying to re-run to see if they were spurious

@suzubara Looks like most of those went away after re-running.

That's really odd. The legitimate diffs with missing graphics appear to be in Edge. I noticed on the breadcrumb PR that the carets between breadcrumbs were rendering as squares in edge in Happo as well.

The accordion diff is weird. It looks like Happo is capturing screenshots while hovering over elements:

[suzubara]

yeah that is weird, I haven't seen that before. I would chalk it up to Happo since the components themselves look fine