Remove radix-vue dependency

[pascalbaljet]

This PR removes radix-vue from the Vue version and adds focus-trap, which is a popular, well-maintained, framework-agnostic library. I want to move away from radix-vue, as it has some advantages:

• No more required DialogTitle component.
• It makes it easier to implement new features in the future, such as draggable modals.
• It reduces the UMD build from 52.73 kB (15.93 kB gzipped) to 40.32 kB (12.60 kB gzipped).

Still draft because I'm investigating whether we can move away from @headlessui/react in the React version as well. Then we could use focus-trap there as well and make the two versions much more consistent.