docs: Add migration guide for h rendering registered component (#1927)

[Fiv5]

Description of Problem

In v3.x, h now no longer use a string ID (e.g. h('some-component')) to implicitly lookup globally registered components. It may explicitly show on the Migration Guide Docs.

Proposed Solution

Update the Migration Guide.

Additional Information

[NataliaTepluhina]

@Fiv5 thank you for adding this contribution! I've left a few suggestions (mostly on wording/code formatting), rest looks good to me 👍🏻

[NataliaTepluhina]

Suggested change

	In 2.x, when a component has been registered, the render function will work well when passing the component's name as string to the first arguments:
	In 2.x, when a component has been registered, the render function would work well when passing the component's name as a string to the first argument:

[NataliaTepluhina]

Suggested change

	template: '<button @click="count++">Clicked {{ count }} times.</button>'
	template: `
	<button @click="count++">
	Clicked {{ count }} times.
	</button>
	`

[NataliaTepluhina]

Suggested change

	In 3.x, with VNodes being context-free, we can no longer use a string ID to implicitly lookup registered components. Instead, we need to use an imported API:
	In 3.x, with VNodes being context-free, we can no longer use a string ID to implicitly lookup registered components. Instead, we need to use an imported `resolveComponent` method:

[Fiv5]

Thanks for the valuable suggestions!

[skirtles-code]

I think you'd get a warning calling it like this:

[Vue warn]: resolveComponent can only be used in render() or setup().

[Fiv5]

Sorry, I will double-check the examples provided.

[skirtles-code]

There seems to be a small inconsistency here. The rest of this example is using Vue.h but this line uses an imported resolveComponent rather than Vue.resolveComponent.

[skirtles-code]

I don't believe package-lock.json should be included in this PR.