Vue 3 support

[rigma]

With the eminent release of Vue 3, and because it's a requested feature in #230, this PR introduces Vue 3 support for vue-fontawesome.

Changes made in the PR

Converting functional components into stateful components

With the release of Vue 3, { functional: true } component option is removed and performances between functional and stateful components are now negligeable.

As recommanded in the migration guide, components are now stateful.

Using setup() functions instead of render() functions

⚠️ Breaking changes ⚠️

In Vue 3, render functions will no longer receives arguments. As a result, it can no longer access to props or slots and the h function shall be globally imported.

A more detailed explanation of the changes can be found in the related RFC: vuejs/rfcs#28.

Therefore, I've updated the conversion function from converter.js to return render functions that can be used with setup() method of a component.

Refreshing example

I've rewritten the example to showcase the use of vue-fontawesome with Vue 3.

Migrating Jest test cases

Now, the test cases are using @vue/test-utils in order to mount components.

Closes #230

[robmadole]

Amazing! Thanks @rigma. I will have some time in the next couple of weeks to look over this and move it forward.

[robmadole]

Alright, I'm focusing on this today. I expect to have an pre-release candidate out today from your work @rigma

[robmadole]

Hey, @rigma I'm prepped to merge this in but I introduced a couple of package lock conflicts. Do you think you can resolve those real quick? (The examples/vue-cli-webpack just needs to be deleted.) Otherwise if you don't have time I can open another PR and pull your commits over.

[robmadole]

@rigma porting this over to #249. I want to make sure I can get this released today!

[rigma]

No worries @robmadole! If you want me to do some changes, I can made it.

[robmadole]

Nope, you've done plenty! Thank you again.