feat(loaders): introduce Inline component

[austingreendev]

Description

This is the v1 of a "vertical space neutral" typing indicator component. @allisonacs could you help me with the naming here? Not sure if we need to generalize this name for other uses in the future.

Detail

This component uses the CSS pulse animation from the original self-service implementation with the following changes:

• The SVG circles are now defaulted to 0.2 opacity to avoid a "flash of unstyled content"
• It now supports RTL mode via our ThemeProvider
• Size and color are now calculated in CSS-in-JS so can be provided via props

Default size: 16px
Default color: grey-600

LTR

RTL

Accessibility

For loading indicators, the aria-busy and aria-live attributes must be applied to containing elements and have to be managed by consumers (same as the other loading components).

Checklist

• 👌 design updates are Garden Designer approved (add the
  designer as a reviewer)
• 💅 view component styling is based on a Garden CSS
  component
• 🌐 Styleguidist demo is up-to-date (yarn start)
• ⬅️ renders as expected with reversed (RTL) direction
• ♿ analyzed via axe and evaluated using VoiceOver
• 💂‍♂️ includes new unit and snapshot tests
• 📝 tested in Chrome, Firefox, Safari, Edge, and IE11

[coveralls]

Coverage increased (+0.03%) to 93.542% when pulling d301263 on agreen/typing-indicator into 218b0c2 on master.

[austingreendev]

Pre-published for review at https://garden.zendesk.com/react-components/loaders/

[ryanseddon]

Looks good only minor feedback