Fix #400, RSP-709, RSP-710, RSP-711, RSP-712 [Accessibility][Documentation] Search, SearchWithin, Select, SelectList (#401)
Fixes:
- #400 [Accessibility] SearchWithin: improve labelling of child Search and Select controls
- RSP-709 [Accessibility][Documentation] Search
- RSP-710 [Accessibility][Documentation] SearchWithin
- RSP-711 [Accessibility][Documentation] Select
- RSP-712 [Accessibility][Documentation] SelectList
What changed:
1. Search input should have `type="search"`.
2. Refactor `aria-label` and `aria-labelledby` props in SearchWithin.
3. Added `autoFocus` prop to SearchWithin, so that search input will support `autoFocus`.
4. Refactor `aria-label` prop for Select.
5. Fix SelectList story for `renderItem` so that it behaves as described.
6. Update tests for Search, SearchWithin, Select and SelectList, improving coverage
7. Update documentation for Search, SearchWithin, Select and SelectList
8. Correct Heading `variant` and `aria-level` props in documentation.