[Discover] Add unsaved changes modal (#218500) (#225252)

## Summary

Closes #218500

When there are unsaved changes in Discover a modal will prompt the user
to either risk losing them or not leaving the page.


https://github.com/user-attachments/assets/c516b3a7-0954-496b-8494-574ba8547d27

### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [x] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/src/platform/packages/shared/kbn-i18n/README.md)
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] The PR description includes the appropriate Release Notes section,
and the correct `release_note:*` label is applied per the
[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)

---------

Co-authored-by: kibanamachine <[email protected]>

Author: AlexGPlay

src/platform/plugins/shared/discover/public/__mocks__/discover_state.mock.ts

@@ -44,7 +44,7 @@ export function getDiscoverStateMock({
   history?: History<HistoryLocationState>;
   customizationContext?: DiscoverCustomizationContext;
   services?: DiscoverServices;
-}) {
+} = {}) {
   if (!history) {
     history = createBrowserHistory<HistoryLocationState>();
     history.push('/');

src/platform/plugins/shared/discover/public/application/discover_router.test.tsx

@@ -47,7 +47,7 @@ const renderWithRouter = (path: string) => {
   });
   render(
     <Router history={history}>
-      <DiscoverRoutes customizationContext={mockCustomizationContext} />
+      <DiscoverRoutes onAppLeave={jest.fn()} customizationContext={mockCustomizationContext} />
     </Router>
   );
 

src/platform/plugins/shared/discover/public/application/discover_router.tsx

@@ -12,6 +12,7 @@ import { Router, Routes, Route } from '@kbn/shared-ux-router';
 import React from 'react';
 import { EuiErrorBoundary } from '@elastic/eui';
 import { KibanaContextProvider } from '@kbn/kibana-react-plugin/public';
+import type { AppMountParameters } from '@kbn/core/public';
 import { ContextAppRoute } from './context';
 import { SingleDocRoute } from './doc';
 import { NotFoundRoute } from './not_found';
@@ -23,6 +24,7 @@ import { DiscoverMainRoute } from './main';
 export interface DiscoverRouterProps {
   services: DiscoverServices;
   customizationContext: DiscoverCustomizationContext;
+  onAppLeave: AppMountParameters['onAppLeave'];
 }
 
 export const DiscoverRouter = ({ services, ...routeProps }: DiscoverRouterProps) => {
@@ -40,7 +42,7 @@ export const DiscoverRouter = ({ services, ...routeProps }: DiscoverRouterProps)
 // this exists as a separate component to allow the tests to gather the routes
 export const DiscoverRoutes = ({
   ...routeProps
-}: Pick<DiscoverRouterProps, 'customizationContext'>) => {
+}: Pick<DiscoverRouterProps, 'customizationContext' | 'onAppLeave'>) => {
   return (
     <Routes>
       <Route path="/context/:dataViewId/:id">

src/platform/plugins/shared/discover/public/application/index.tsx

@@ -10,17 +10,24 @@
 import React from 'react';
 import { i18n } from '@kbn/i18n';
 import { toMountPoint } from '@kbn/react-kibana-mount';
+import type { AppMountParameters } from '@kbn/core/public';
 import { DiscoverRouter } from './discover_router';
 import type { DiscoverServices } from '../build_services';
 import type { DiscoverCustomizationContext } from '../customizations';
 
 export interface RenderAppProps {
   element: HTMLElement;
+  onAppLeave: AppMountParameters['onAppLeave'];
   services: DiscoverServices;
   customizationContext: DiscoverCustomizationContext;
 }
 
-export const renderApp = ({ element, services, customizationContext }: RenderAppProps) => {
+export const renderApp = ({
+  element,
+  onAppLeave,
+  services,
+  customizationContext,
+}: RenderAppProps) => {
   const { capabilities, chrome, data, core } = services;
 
   if (!capabilities.discover_v2.save) {
@@ -36,7 +43,11 @@ export const renderApp = ({ element, services, customizationContext }: RenderApp
   }
 
   const unmount = toMountPoint(
-    <DiscoverRouter services={services} customizationContext={customizationContext} />,
+    <DiscoverRouter
+      onAppLeave={onAppLeave}
+      services={services}
+      customizationContext={customizationContext}
+    />,
     core
   )(element);