FocusHost type is not exported + PR

[riovir]

This issue is similar to #1903.

Expected behavior

import type { FocusHost } from '@lion/ui/types/form-core.js'; would work.

Actual Behavior

Type error, as the type is not exported.

Additional context

This blocks a bundler from generating a valid index.d.ts for components directly using the FocusMixin.

[riovir]

Submitted PR here: #2367