Add `useBreakpoint` composable

[TylerAPfledderer]

Feature request

Add the useBreakpoint composable to the Vue package.

This is an existing function from the React package to retrieve the current responsive media breakpoint. Returns the token name from the theme config.

🚨 Important

This depends on the useMediaQuery, based on the hook from the React package (See Issue #182). However, it is suggested to use the version of the composable from the VueUse library.