[Discover] Redesign for the grid, panels and sidebar v1 (#165866)

## Summary

### Part 1

- Resolves https://github.com/elastic/kibana/issues/164287
- Closes https://github.com/elastic/kibana/issues/146339
- Previously separate PR https://github.com/elastic/kibana/pull/164187

Changes:
- ~~swaps checkbox and row selection~~
- removes vertical borders
- adds rows highlight
- increases cell padding
- adds row stripes
- updates header background
- removes grey background from field name and makes it bolder (part of
https://github.com/elastic/kibana/issues/164634)
- updates Surrounding Documents side paddings

### Part 2

- Resolves https://github.com/elastic/kibana/issues/164661
- Previously separate PR https://github.com/elastic/kibana/pull/165687

Changes:
- removes background from panels, tabs and sidebar
- updates "Add a field" button style
- removes shadow from field list items
- makes field search compact

### Part 3

- Resolves https://github.com/elastic/kibana/issues/164662

Changes:
- wraps "Add a field" button in its own container with a top border
- ~~adds a drag handle to sidebar items~~
- ~~adds new Show/Hide buttons to toggle sidebar~~ moves sidebar toggle
button from discover plugin to unified field list
- reduces spaces between sidebar items from 4px to 2px
- reduces padding on Single Document page
- removes border above grid tabs

<img width="600" alt="Screenshot 2023-09-07 at 14 39 48"
src="976db247-fd70-4c9b-8634-552ece45b522">


Please note that "auto" row height is in a separate PR which is also
ready for review https://github.com/elastic/kibana/pull/164218

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>
Co-authored-by: Davis McPhee <davismcphee@hotmail.com>
Co-authored-by: Davis McPhee <davis.mcphee@elastic.co>

examples/unified_field_list_examples/public/field_list_sidebar.tsx

@@ -33,6 +33,8 @@ const getCreationOptions: UnifiedFieldListSidebarContainerProps['getCreationOpti
     originatingApp: PLUGIN_ID,
     localStorageKeyPrefix: 'examples',
     timeRangeUpdatesType: 'timefilter',
+    compressed: true,
+    showSidebarToggleButton: true,
     disablePopularFields: true,
   };
 };