New Spinner component

[bernardojoaogarcia]

Add new Spinner component to the Topbar. Either contribute new spinner component to Polaris internal or keep it isolated for topbar for the time being.

We will need to change the color of the spinner depending on where it is used. This should be baked into the component that is using it because of one off contextual changes. Admin UI foundations UX work is aligned with this.

[alex-page]

Consider this timeless design

[bernardojoaogarcia]

Here is some progress work to unify tokens for the new spinner. I'll review these concepts beginning of next week with @sarahill

[sophschneider]

moving this to ice box as we are discussing if this is worth investing in now or waiting for ui foundations