Add event hooks to nuxt-loading component

[btkostner]

Is your feature request related to a problem? Please describe.

I have some async data being loaded in fetch. I want to scroll on the page after all content is loaded. The easiest way seemed to be something like this.$loading.$once('finished').

Describe the solution you'd like

I'd like some events added to the nuxt-loading component so people can use it as the source of truth if stuff is still being loaded. The only one I am concerned about is finished, but I could see some others added as well.

Describe alternatives you've considered

Not using the component as the single source of truth. This can be more accurate, but also takes more work. Using the nuxt-loading component is fast, has good support with things like axios already, and is pretty simple to use.

[danielroe]

Let's track progress via #14221.