Improve Finder ajax error handling

[Fedik]

Pull Request for Issue #39717 and #39965 .

Summary of Changes

Catch broken json and show an error message.
For Finder indexer, and for Finder autocomplete.

Testing Instructions

Apply patch, run npm install.

1. Repeat test from [5.0] Smart Search: Improving error handling of Indexing #39965
   Go to a finder plugin, for example /plugins/finder/content/src/Extension/Content.php and trigger any output in the index() method. For example you can add var_dump($item->title).
   In the Smart Search component in the backend click on "Index".

2. And similar for Autocomplete.
   Add var_dump(['error']) somewhere here

   joomla-cms/components/com_finder/src/Controller/SuggestionsController.php

   Lines 34 to 38 in 10f250f

   	public function suggest()
   	{
   	$app = $this->app;
   	$app->mimeType = 'application/json';

   
   Make sure autocomplete is enabled, then go to site search page, and try to search something.

Actual result BEFORE applying this Pull Request

The ajax stops without any visible signs of life.

Expected result AFTER applying this Pull Request

You should get an error message.

Link to documentations

Please select:

• No documentation changes for docs.joomla.org needed
• No documentation changes for manual.joomla.org needed

[chmst]

I am confused .. @Fedik this is for 4.2 while @Hackwar has a PR for 4.3.

I have tested this PR on a 4.2 multilingual with blog sample data. But the output freezes without error message.
Need to find out why the npm ci did not do the job on the dev branch.

Repeated the test with the prebuild package and got a message

[chmst]

I have tested this item ✅ successfully on 5d37ee4

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[Quy]

I have tested this item ✅ successfully on 5d37ee4

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/39973.}

[Quy]

RTC

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[roland-d]

Thank you