Vue 3: Composition API refactor proposal

[Megarsh]

I’d like to suggest a small refactor for the Vue 3 package.

I converted the remaining Options API components to the Composition API in:

• packages/vue3/src/head.ts
• packages/vue3/src/whenVisible.ts
• packages/vue3/src/deferred.ts

There's one remaining mixin with Options Api - packages/vue3/src/remember.ts which I haven't changed because I don't know its usage.

The main reason for this is to make it possible to run the package without the Options API, and to reduce reliance on patterns like getCurrentInstance() / app.config.globalProperties, which will help with future Vue Vapor compatibility (which I hope will be considered when it's released).

Here is the commit with the changes:
Megarsh@b4219d3

If this looks useful, I can open a PR against the appropriate branch and adjust based on feedback.