Rewrite TS usage guide page
Rewrite TS usage guide page

- Dropped legacy section that showed use of action type unions and
  hand-written action creators
- Copied TS quick start section from RTK docs
- Added "what you'll learn / prerequisites" boxes
- Added additional details for typing reducers / thunks / middleware
- Removed now-duplicate RTK usage info
- Added additional RTK common usage patterns info
- Added "recommendations" section

gaearon/redux,gaearon/redux