Add Loading spinner to components

[spences10]

Is your feature request related to a problem? Please describe.
When the components come into view, although they have their height set they are essentially empty until the embed loads.

Describe the solution you'd like
Add a loading spinner to show in the place of the empty space.

[paoloricciuti]

I might take a look at this as soon as I have time if is still Todo.

[spences10]

Yeah, still on the todo list 😄

[raulfdm]

+1 for that.

I'd say not only adding a spinner but allowing users to pass a slot that would be rendered while loading:

<Tweet tweetId="1234">
  <MyLoader slot="load" />
</Tweet>