refactor: improvements after removing simplebar dep

[vanbasten17]

This is a continuation of: https://github.com/hubtype/botonic/pull/2900 Several things done here:

• Remove scrollable-content generic component and create it for each scrollable div.
• Add notable refs (webchatRef, chatAreaRef, headerRef) in WebchatContext to be accessed from different parts of the coee
• Remove JS commented code already migrated to TS.
• Reduce util/dom.js in favour of using new hooks.
• Migrate from JS to TS:
  • device-adapter
  • scrollbar-controller
  • webchat-resizer
• Simplify WebchatHeader component
• New hooks:
  • useScrollToBottom: centralize logic for scrolling to the end of scrollable messages list container
  • useVirtualKeyboardDetection: detect whether virtual keyboard is open or not (iOS/Safari)
  • useWebchatDimensions: recalculation of webchat / chat area heights
• Create a new component WebchatChatArea
• Set textarea fontsize to 16px to be consistent with the rest of styles and avoid auto-focusing issues on iOS.