bug #37000 Add meaningful message when using ProcessHelper and Process is not installed (l-vo)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead.

Discussion
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Add meaningful message when using ProcessHelper and Process is not installed

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       |
| License       | MIT
| Doc PR        |

When using the process helper without the `Process` component, a php fatal error is triggered (`PHP Fatal error:  Uncaught Error: Class 'Symfony\Component\Process\Process' not found`). This PR adds a meaningful exception; allowing to display a console error message instead of a raw php fatal error.

Commits
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3ab76e40ff Add meaningful message when Process is not installed (ProcessHelper)

src/Symfony/Component/Console/Helper/ProcessHelper.php

@@ -37,6 +37,10 @@ class ProcessHelper extends Helper
      */
     public function run(OutputInterface $output, $cmd, $error = null, callable $callback = null, $verbosity = OutputInterface::VERBOSITY_VERY_VERBOSE)
     {
+        if (!class_exists(Process::class)) {
+            throw new \LogicException('The Process helper requires the "Process" component. Install "symfony/process" to use it.');
+        }
+
         if ($output instanceof ConsoleOutputInterface) {
             $output = $output->getErrorOutput();
         }