[Investigations] - Timeline tabs file cleanup (#179832)

## Summary

This PR cleans up a bit of the code around timeline tabs. It de-dupes
the layout components and some of the shared functionality between the
tabs. I would also like to move the tabs from using the `connector`
pattern to using `useSelector`, but that'll be done in a follow up PR.
The commit history unfortunately pulls in a bit from [this
pr](#176064), but the 2 commits
for the actual files changed in this PR are as follows:

1. (No code changes, just moving files) Moving the tabs into a nested
tabs folder:
89fa2d8

2. (Actual Code Changes) De-duping the shared components:
c6eecdb

3. (No code changes, moving filed and renaming) Removed the `_content`
parts of the folder names, and moved the `tabs_content` files into the
`tabs` folder:
ec3b959

---------

Co-authored-by: Jatin Kathuria <jatin.kathuria@elastic.co>
Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

x-pack/plugins/security_solution/public/assistant/send_to_timeline/index.tsx

@@ -34,8 +34,8 @@ import {
 import { useDiscoverInTimelineContext } from '../../common/components/discover_in_timeline/use_discover_in_timeline_context';
 import { useShowTimeline } from '../../common/utils/timeline/use_show_timeline';
 import { useIsExperimentalFeatureEnabled } from '../../common/hooks/use_experimental_features';
-import { useDiscoverState } from '../../timelines/components/timeline/esql_tab_content/use_discover_state';
 import { useSourcererDataView } from '../../common/containers/sourcerer';
+import { useDiscoverState } from '../../timelines/components/timeline/tabs/esql/use_discover_state';
 
 export interface SendToTimelineButtonProps {
   asEmptyButton: boolean;

x-pack/plugins/security_solution/public/common/components/discover_in_timeline/use_discover_in_timeline_actions.tsx

@@ -15,14 +15,14 @@ import type { SavedSearch } from '@kbn/saved-search-plugin/common';
 import type { DiscoverAppState } from '@kbn/discover-plugin/public/application/main/services/discover_app_state_container';
 import type { TimeRange } from '@kbn/es-query';
 import { useMutation, useQueryClient } from '@tanstack/react-query';
-import { useDiscoverState } from '../../../timelines/components/timeline/esql_tab_content/use_discover_state';
+import { useDiscoverState } from '../../../timelines/components/timeline/tabs/esql/use_discover_state';
 import { timelineDefaults } from '../../../timelines/store/defaults';
 import { TimelineId } from '../../../../common/types';
 import { timelineActions, timelineSelectors } from '../../../timelines/store';
 import { useAppToasts } from '../../hooks/use_app_toasts';
 import { useShallowEqualSelector } from '../../hooks/use_selector';
 import { useKibana } from '../../lib/kibana';
-import { savedSearchComparator } from '../../../timelines/components/timeline/esql_tab_content/utils';
+import { savedSearchComparator } from '../../../timelines/components/timeline/tabs/esql/utils';
 import {
   DISCOVER_SEARCH_SAVE_ERROR_TITLE,
   DISCOVER_SEARCH_SAVE_ERROR_UNKNOWN,

x-pack/plugins/security_solution/public/common/components/events_viewer/index.tsx

@@ -59,7 +59,7 @@ import { useFieldBrowserOptions } from '../../../timelines/components/fields_bro
 import {
   useSessionViewNavigation,
   useSessionView,
-} from '../../../timelines/components/timeline/session_tab_content/use_session_view';
+} from '../../../timelines/components/timeline/tabs/session/use_session_view';
 import {
   EventsContainerLoading,
   FullScreenContainer,

x-pack/plugins/security_solution/public/detections/components/alerts_table/index.tsx

@@ -31,7 +31,7 @@ import { GraphOverlay } from '../../../timelines/components/graph_overlay';
 import {
   useSessionView,
   useSessionViewNavigation,
-} from '../../../timelines/components/timeline/session_tab_content/use_session_view';
+} from '../../../timelines/components/timeline/tabs/session/use_session_view';
 import { inputsSelectors } from '../../../common/store';
 import { combineQueries } from '../../../common/lib/kuery';
 import { useInvalidFilterQuery } from '../../../common/hooks/use_invalid_filter_query';

x-pack/plugins/security_solution/public/detections/containers/detection_engine/alerts/use_signal_index.test.tsx

@@ -16,7 +16,7 @@ import { sourcererSelectors } from '../../../../common/store';
 jest.mock('./api');
 jest.mock('../../../../common/hooks/use_app_toasts');
 jest.mock('../../../../common/components/user_privileges/endpoint/use_endpoint_privileges');
-jest.mock('../../../../timelines/components/timeline/esql_tab_content');
+jest.mock('../../../../timelines/components/timeline/tabs/esql');
 
 describe('useSignalIndex', () => {
   let appToastsMock: jest.Mocked<ReturnType<typeof useAppToastsMock.create>>;

x-pack/plugins/security_solution/public/timelines/components/open_timeline/note_previews/index.tsx

@@ -31,7 +31,7 @@ import { useDeepEqualSelector } from '../../../../common/hooks/use_selector';
 import { SourcererScopeName } from '../../../../common/store/sourcerer/model';
 import { useSourcererDataView } from '../../../../common/containers/sourcerer';
 import { useDeleteNote } from './hooks/use_delete_note';
-import { getTimelineNoteSelector } from '../../timeline/notes_tab_content/selectors';
+import { getTimelineNoteSelector } from '../../timeline/tabs/notes/selectors';
 
 export const NotePreviewsContainer = styled.section`
   padding-top: ${({ theme }) => `${theme.eui.euiSizeS}`};