feat(Modal): add isFullWidth prop

[tw15egan]

Closes #11933

Adds a new isFullWIdth prop that removes any margin and padding placed on the modal-content class.

Changelog

New

• isFullWidth prop and associated styles for Modal and ComposedModal that removes margin and padding.
• e2e tests added to catch regressions
• updated snapshots

Testing / Reviewing

Was unsure if we also wanted to remove the padding/margin from the headers; for now they are still there because they match the spec images

• Go to ComposedModal and Modal and ensure the Full Width example matches the spec images.

[netlify]

✅ Deploy Preview for carbon-components-react ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	fc9a2dd
🔍 Latest deploy log	https://app.netlify.com/sites/carbon-components-react/deploys/6363b008df12150009ba8c09
😎 Deploy Preview	https://deploy-preview-12462--carbon-components-react.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[netlify]

✅ Deploy Preview for carbon-elements ready!

Name	Link
🔨 Latest commit	fc9a2dd
🔍 Latest deploy log	https://app.netlify.com/sites/carbon-elements/deploys/6363b00851fc4d0008cefc00
😎 Deploy Preview	https://deploy-preview-12462--carbon-elements.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[aagonzales]

The full-width stories look good, but I had a follow-up question after seeing the Playground example. Would a user be able to mix full width and the indented style? Or is it an either-or situation? Like below

[tw15egan]

I think they would still be able to do that; they would just have to add padding independently. This just removes any padding we ship to prevent our styles from blocking any designs since we only place padding on the modal body container.

[shixiedesign]

Thank you! Looks great and thanks for the ⚡ speed. I'm wondering if this creates additional work for @carbon-design-system/carbon-platform-designers to add guidance on when to use the isFullwidth prop...? This PR looks good to me though! Thank you!

[aagonzales]

You bring up a good point @shixiedesign we need to add guidance on the website now. It would actually be the system squad who adds it (platform is pulling markdown from the original site atm). I've made an issue so we don't forget.

[tay1orjones]

Looks great!