ui.activity_stream

via @sandruparo

## Design

[design url](https://xd.adobe.com/view/eebb600c-026b-4ca1-bb6b-0a439235452b-bbe8/specs/)

## Proposed API
```ts
interface ActivityState {
/** State text **/
text: S
/** Tag background color. **/
color?: S
}

interface ActivityStreamItem {
/** The activity title. **/
title: S
/** The caption, displayed below the title. **/
caption: S
/** Original state identifier. **/
from?: ActivityState
/** Final state identifier. **/
to?: ActivityState
}

interface ActivityStream {
/** The card's title **/
title: S
/** The activities listed in this card. **/
items: ActivityStreamItem[]
}
```

cc @lo5