Alert component follow-up

[bmdalex]

Alert component follow-up

Alert component was created in #1063 there are a few things we need to follow up on:

• make Alert an auto controlled component (feat(alert): v1 #1063 (comment))
• adapt v2 API:
  • header (feat(alert): v1 #1063 (comment))
  • other intent props (error, negative)

interface AlertPropsV2 extends AlertProps {
  /** The title of the alert **/
  header?: string

  /** An alert may be formatted to display an error or negative message. */
  error?: boolean
  negative?: boolean // EXPERIMENTAL - not sure we will add both

  /** An alert may be formatted to display a positive message. */
  positive?: boolean // EXPERIMENTAL - synonym for success  not sure we will add it
  
  /** Defines whether Alert is displayed. */
  open?: boolean

  /** Event for request to change 'open' value. */
  onOpenChange?: ComponentEventHandler<PopupProps>

  /** EXPERIMENTAL - some Alerts might need different style for all types/intents */
  appearance?: 'basic' | 'card'
}

• implement other themes
• add visual tests in other themes
• remove display flex so that children are displayed on different lines (see: https://codesandbox.io/s/xr52j56xxz?module=/example.js) suggested by @layershifter

[jurokapsiar]

this is not required anymore.