[NO JIRA]: Update popover fallback to align with floating-ui

[olliecurtis]

This PR updates the fallback return value for the renderTarget property due to a change in @floating-ui/[email protected].

fix(FloatingPortal): allow root to be reactive from null to an element. ⚠️ an always-null value will never render a portal node as this indicates it's waiting for an element; it must be undefined

When the value is set to be () => null it will never render the popover and mean that it can never be displayed.

This PR also removes old .d.ts files as these are autogenerated at the build and aren't needed

[github-actions]

Visit https://backpack.github.io/storybook-prs/3700 to see this build running in a browser.

[github-actions]

	Warnings
⚠️	Package source files (e.g. packages/package-name/src/Component.js) were updated, but snapshots weren't. Have you checked that the tests still pass?
⚠️	Package source files (e.g. packages/package-name/src/Component.tsx) were updated, but type files weren't. Have you checked that no types have changed?

Browser support

If this is a visual change, make sure you've tested it in multiple browsers.

Generated by 🚫 dangerJS against b0eef32