support for Vue3

[fusionswap]

Hi,

Is there Vue3 version for this vue-tree-list.

I tried to poc this with Vue3. I get error in the beforeCreate lifecycle hook in VueTreeList.vue at this line
this.$options.components.item = require('./VueTreeList').default

Browser logs says
Uncaught (in promise) TypeError: Cannot set property 'item' of undefined
at Proxy.beforeCreate (JsonSchemaTree.vue?2fce:218)
at callWithErrorHandling (runtime-core.esm-bundler.js?5c40:154)
at callWithAsyncErrorHandling (runtime-core.esm-bundler.js?5c40:163)
at callSyncHook (runtime-core.esm-bundler.js?5c40:5710)
at applyOptions (runtime-core.esm-bundler.js?5c40:5491)
at finishComponentSetup (runtime-core.esm-bundler.js?5c40:6309)
at setupStatefulComponent (runtime-core.esm-bundler.js?5c40:6245)
at setupComponent (runtime-core.esm-bundler.js?5c40:6185)
at mountComponent (runtime-core.esm-bundler.js?5c40:3960)
at processComponent (runtime-core.esm-bundler.js?5c40:3936)

this.$options.components is undefined in this case.

[tobiasdiez]

@ParadeTo any update on this issue? Would you except a PR that provides vue3 support?