feat: support vue3

[tobiasdiez]

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Fixes https://github.com/jamesxwang/vue-hotspot/issues/126 by using vue-demi.

I think, in general both the vue 2 and vue 3 version are now working. There are a few strange vm.watcher is undefined errors in the browser console for me, where I don't know where they come from. Moreover, the setup is a bit complicated since the vue-cli/rollup setup is deprecated and one should now move to vite. But maybe as a first version this is good enough, and as a second step one could maybe migrate to a cleaner setup (e.g. yarn workspaces, with separate vue2 + vue3 demos, every build by vite etc). What do you think?

One other general question would be if you want to continue vue 2 at all, or if one could say that the latest release is the last one supporting vue2, from now on its only vue3.

[jamesxwang]

Hi @tobiasdiez, thanks for your contribution and love for this project, left some comments as the npm run serve threw some errors in the browser console and seems the demo is broken

[jamesxwang]

Also, I played around with this package and found that the vm.watcher error you mentioned comes from the watch function. Still investigating

[tobiasdiez]

I continued working on it and now its somehow working, except that all reactive things are actually static in vue3...

So I was wondering if you actually want to continue supporting vue2 with new updates/fixes, or if it would be okay to completely switch over to vue3. I feel this would definitively ease development. What do you think?