[search] avoid loading searchNavigation.chunk on on every page load (#209818)

Part of #194171

PR removes all async imports run during searchNavigation plugin setup
and start methods.

### Test instructions
* Start kibana locally
* Open network tab in browser
* Open home page. Verify `searchNavigation.chunk` are not loaded. The
screen shots show the behavior in main where `searchNavigation.chunk`
are loaded on home page
<img width="600" alt="Screenshot 2025-02-05 at 9 20 21 AM"
src="https://github.com/user-attachments/assets/e718e18e-de6e-4c1e-ba28-af713440459c"
/>

---------

Co-authored-by: Elastic Machine <[email protected]>

Author: nreese

x-pack/solutions/search/plugins/search_solution/search_navigation/public/classic_navigation.ts

@@ -11,13 +11,13 @@ import type { CoreStart, ScopedHistory } from '@kbn/core/public';
 import type { ChromeNavLink, EuiSideNavItemTypeEnhanced } from '@kbn/core-chrome-browser';
 import type { SolutionNavProps } from '@kbn/shared-ux-page-solution-nav';
 
-import type { ClassicNavItem, ClassicNavItemDeepLink, ClassicNavigationFactoryFn } from './types';
+import type { ClassicNavItem, ClassicNavItemDeepLink } from './types';
 import { stripTrailingSlash } from './utils';
 
 type DeepLinksMap = Record<string, ChromeNavLink | undefined>;
 type SolutionNavItems = SolutionNavProps['items'];
 
-export const classicNavigationFactory: ClassicNavigationFactoryFn = (
+export const classicNavigationFactory = (
   classicItems: ClassicNavItem[],
   core: CoreStart,
   history: ScopedHistory<unknown>

x-pack/solutions/search/plugins/search_solution/search_navigation/public/plugin.ts

@@ -20,10 +20,10 @@ import type {
   SearchNavigationPluginSetup,
   SearchNavigationPluginStart,
   ClassicNavItem,
-  ClassicNavigationFactoryFn,
   SearchNavigationSetBreadcrumbsOptions,
   AppPluginStartDependencies,
 } from './types';
+import { classicNavigationFactory } from './classic_navigation';
 
 export class SearchNavigationPlugin
   implements Plugin<SearchNavigationPluginSetup, SearchNavigationPluginStart>
@@ -33,7 +33,6 @@ export class SearchNavigationPlugin
   private baseClassicNavItemsFn: (() => ClassicNavItem[]) | undefined = undefined;
   private coreStart: CoreStart | undefined = undefined;
   private pluginsStart: AppPluginStartDependencies | undefined = undefined;
-  private classicNavFactory: ClassicNavigationFactoryFn | undefined = undefined;
   private onAppMountHandlers: Array<() => Promise<void>> = [];
   private chromeSub: Subscription | undefined;
 
@@ -52,10 +51,6 @@ export class SearchNavigationPlugin
       this.currentChromeStyle = value;
     });
 
-    import('./classic_navigation').then(({ classicNavigationFactory }) => {
-      this.classicNavFactory = classicNavigationFactory;
-    });
-
     return {
       handleOnAppMount: this.handleOnAppMount.bind(this),
       registerOnAppMountHandler: this.registerOnAppMountHandler.bind(this),
@@ -97,13 +92,12 @@ export class SearchNavigationPlugin
   private useClassicNavigation(history: ScopedHistory<unknown>) {
     if (
       this.baseClassicNavItemsFn === undefined ||
-      this.classicNavFactory === undefined ||
       this.coreStart === undefined ||
       this.currentChromeStyle !== 'classic'
     )
       return undefined;
 
-    return this.classicNavFactory(this.baseClassicNavItemsFn(), this.coreStart, history);
+    return classicNavigationFactory(this.baseClassicNavItemsFn(), this.coreStart, history);
   }
 
   private setBreadcrumbs(

x-pack/solutions/search/plugins/search_solution/search_navigation/public/types.ts

@@ -7,7 +7,7 @@
 
 import type { ReactNode } from 'react';
 import type { AppDeepLinkId, ChromeBreadcrumb } from '@kbn/core-chrome-browser';
-import type { CoreStart, ScopedHistory } from '@kbn/core/public';
+import type { ScopedHistory } from '@kbn/core/public';
 import type { ServerlessPluginSetup, ServerlessPluginStart } from '@kbn/serverless/public';
 import type { SolutionNavProps } from '@kbn/shared-ux-page-solution-nav';
 
@@ -51,12 +51,6 @@ export interface ClassicNavItem {
   name?: ReactNode;
 }
 
-export type ClassicNavigationFactoryFn = (
-  items: ClassicNavItem[],
-  core: CoreStart,
-  history: ScopedHistory<unknown>
-) => SolutionNavProps | undefined;
-
 export interface SearchNavigationSetBreadcrumbsOptions {
   // When set to `true` breadcrumbs are only set when chrome style is set to classic.
   // This option is for pages who rely on Solution Navigation for breadcrumbs, but still