Use render instead of createApp when rendering vdom

[larrifax]

When rendering Vue components inside of <template #eventContent></template>, the Vue components aren't rendered within the main Vue application's context, but in a new Vue application created by the following function:

fullcalendar-vue/src/custom-content-type.ts

Lines 57 to 76 in d203b0c

	function initVue(initialContent: VNode[], parent: Vue) {
	return new Vue({
	parent,
	data: {
	content: initialContent,
	},
	render(h) {
	let { content } = this
	// the slot result can be an array, but the returned value of a vue component's
	// render method must be a single node.
	if (content.length === 1) {
	return content[0]
	} else {
	return h('span', {}, content)
	}
	}
	})
	}

Since the new Vue application isn't connected to the main Vue application in any way, information about e.g. plugins are lost, making it impossible to use e.g. vue-i18n-next within the rendered components.

I've found a way to overcome this limitation, by patching the library to use render() instead of createApp(), but I'm by no means a Vue expert so I don't know if this is a viable approach or not.

The work is inspired by vuejs/core#2097 (comment) and some of the other comments in the same thread.

[acerix]

Please submit the feature request under Issues, then link this PR to it.

[TheNoim]

Thanks, this is a big performance issue for me.

[keygun-development]

This is also a big performance issue for me, I've just created an issue for this.

[sebastienfontaine]

Please, this is also a big performance issue for me.

[arshaw]

I've recently fixed this performance issue, though via a different technique. I'm using Teleport instead.

See my comment:
#191 (comment)

@larrifax , thank you for the effort you put into this