Modal: fix issue with click outside to dismiss

[shleewhite]

📌 Summary

If merged this PR would update Modal to not use ember-focus-trap to dismiss the Modal on click outside and instead use our own click event.

It also fixes an issue where the scroll bar would get added back if try to close the modal when isDismissDisabled=true.

🛠️ Detailed description

This is necessary because the ember-focus-trap's clickOutSideDeactivates only ever runs once. If a consumer conditionally disables the ability to dismiss the modal, the user may not be able to click outside to deactivate it.

Steps to reproduce:

1. Navigate to: https://hds-showcase.vercel.app/components/modal#demo
2. Click "Open non-dismissable modal"
3. Click outside the modal after it opens, notice it doesn't close and you are able to scroll the page behind the modal.
4. Click "reset isDismissDisabled"
5. Click outside the modal, notice it doesnt close.
6. Click "confirm"/"Cancel"/"close", notice the modal does close.

🔗 External links

Jira ticket: HDS-3972

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👀 Component checklist

• Percy was checked for any visual regression
• A changelog entry was added via Changesets if needed (see templates here)

💬 Please consider using conventional comments when reviewing this PR.

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