[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>

test/functional/apps/discover/group1/_date_nanos_mixed.ts

@@ -15,6 +15,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
   const PageObjects = getPageObjects(['common', 'timePicker', 'discover']);
   const kibanaServer = getService('kibanaServer');
   const security = getService('security');
+  const browser = getService('browser');
   const from = 'Jan 1, 2019 @ 00:00:00.000';
   const to = 'Jan 1, 2019 @ 23:59:59.999';
 
@@ -25,7 +26,11 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       await kibanaServer.importExport.load(
         'test/functional/fixtures/kbn_archiver/date_nanos_mixed'
       );
-      await kibanaServer.uiSettings.replace({ defaultIndex: 'timestamp-*' });
+      await kibanaServer.uiSettings.replace({
+        defaultIndex: 'timestamp-*',
+        hideAnnouncements: true, // should be enough vertical space to render rows
+      });
+      await browser.setWindowSize(1200, 900);
       await security.testUser.setRoles(['kibana_admin', 'kibana_date_nanos_mixed']);
       await PageObjects.common.setTime({ from, to });
       await PageObjects.common.navigateToApp('discover');

test/functional/apps/discover/group1/_discover_histogram.ts

@@ -88,7 +88,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
         return actualCount <= expectedCount;
       });
       const newDurationHours = await PageObjects.timePicker.getTimeDurationInHours();
-      expect(Math.round(newDurationHours)).to.be(26);
+      expect(Math.round(newDurationHours)).to.be(24); // might fail if histogram's width changes
 
       await retry.waitFor('doc table containing the documents of the brushed range', async () => {
         const rowData = await PageObjects.discover.getDocTableField(1);

test/functional/apps/discover/group3/_sidebar.ts

@@ -214,16 +214,19 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
     describe('collapse expand', function () {
       it('should initially be expanded', async function () {
         await testSubjects.existOrFail('discover-sidebar');
+        await testSubjects.existOrFail('fieldList');
       });
 
       it('should collapse when clicked', async function () {
         await PageObjects.discover.toggleSidebarCollapse();
-        await testSubjects.missingOrFail('discover-sidebar');
+        await testSubjects.existOrFail('discover-sidebar');
+        await testSubjects.missingOrFail('fieldList');
       });
 
       it('should expand when clicked', async function () {
         await PageObjects.discover.toggleSidebarCollapse();
         await testSubjects.existOrFail('discover-sidebar');
+        await testSubjects.existOrFail('fieldList');
       });
     });
 

test/functional/page_objects/discover_page.ts

@@ -370,13 +370,14 @@ export class DiscoverPageObject extends FtrService {
   }
 
   public async toggleSidebarCollapse() {
-    return await this.testSubjects.click('collapseSideBarButton');
+    return await this.testSubjects.click('unifiedFieldListSidebar__toggle');
   }
 
   public async closeSidebar() {
     await this.retry.tryForTime(2 * 1000, async () => {
-      await this.toggleSidebarCollapse();
-      await this.testSubjects.missingOrFail('discover-sidebar');
+      await this.testSubjects.click('unifiedFieldListSidebar__toggle-collapse');
+      await this.testSubjects.missingOrFail('unifiedFieldListSidebar__toggle-collapse');
+      await this.testSubjects.missingOrFail('fieldList');
     });
   }