[8.x] improve loading UI in Discover mobile (#197939) (#198457)

# Backport

This will backport the following commits from `main` to `8.x`:
- [improve loading UI in Discover mobile
(#197939)](#197939)

<!--- Backport version: 9.4.3 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sqren/backport)

<!--BACKPORT
[{"author":{"name":"youhonglian","email":"[email protected]"},"sourceCommit":{"committedDate":"2024-10-30T23:41:06Z","message":"improve
loading UI in Discover mobile (#197939)\n\n## Summary\r\n\r\nCloses
https://github.com/elastic/kibana/issues/151503\r\n\r\nIn this PR, use
the EuiEmptyPrompt component to update the loading
UI\r\n\r\n---------\r\n\r\nCo-authored-by: Davis McPhee
<[email protected]>","sha":"7d0f15b160fd2c7bc1d80e62f3499827970fccc1","branchLabelMapping":{"^v9.0.0$":"main","^v8.17.0$":"8.x","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["release_note:skip","💝community","v9.0.0","Team:DataDiscovery","backport:prev-minor"],"title":"improve
loading UI in Discover
mobile","number":197939,"url":"https://github.com/elastic/kibana/pull/197939","mergeCommit":{"message":"improve
loading UI in Discover mobile (#197939)\n\n## Summary\r\n\r\nCloses
https://github.com/elastic/kibana/issues/151503\r\n\r\nIn this PR, use
the EuiEmptyPrompt component to update the loading
UI\r\n\r\n---------\r\n\r\nCo-authored-by: Davis McPhee
<[email protected]>","sha":"7d0f15b160fd2c7bc1d80e62f3499827970fccc1"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.0.0","branchLabelMappingKey":"^v9.0.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/197939","number":197939,"mergeCommit":{"message":"improve
loading UI in Discover mobile (#197939)\n\n## Summary\r\n\r\nCloses
https://github.com/elastic/kibana/issues/151503\r\n\r\nIn this PR, use
the EuiEmptyPrompt component to update the loading
UI\r\n\r\n---------\r\n\r\nCo-authored-by: Davis McPhee
<[email protected]>","sha":"7d0f15b160fd2c7bc1d80e62f3499827970fccc1"}}]}]
BACKPORT-->

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

src/plugins/discover/public/components/common/loading_indicator.tsx

@@ -7,7 +7,7 @@
  * License v3.0 only", or the "Server Side Public License, v 1".
  */
 
-import { EuiFlexGroup, EuiFlexItem, EuiLoadingSpinner, EuiLoadingElastic } from '@elastic/eui';
+import { EuiEmptyPrompt, EuiLoadingSpinner, EuiLoadingElastic } from '@elastic/eui';
 import React from 'react';
 
 interface Props {
@@ -16,10 +16,8 @@ interface Props {
 
 export const LoadingIndicator = ({ type = 'spinner' }: Props) => {
   return (
-    <EuiFlexGroup justifyContent="spaceAround" alignItems="center" gutterSize="none">
-      <EuiFlexItem grow={false}>
-        {type === 'spinner' ? <EuiLoadingSpinner size="l" /> : <EuiLoadingElastic size="xxl" />}
-      </EuiFlexItem>
-    </EuiFlexGroup>
+    <EuiEmptyPrompt
+      icon={type === 'spinner' ? <EuiLoadingSpinner size="l" /> : <EuiLoadingElastic size="xxl" />}
+    />
   );
 };