feature #35673 [Process] Add getter for process starttime (dompie)

This PR was squashed before being merged into the 5.1-dev branch.

Discussion
----------

[Process] Add getter for process starttime

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Tickets       | issue #35531
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->

Add a getter for process start time.

Commits
-------

3b9ed3e378 [Process] Add getter for process starttime

src/Symfony/Component/Process/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+5.1.0
+-----
+
+ * added `Process::getStartTime()` to retrieve the start time of the process as float
+
 5.0.0
 -----
 

src/Symfony/Component/Process/Process.php

@@ -1208,6 +1208,18 @@ class Process implements \IteratorAggregate
         }
     }
 
+    /**
+     * @throws LogicException in case process is not started
+     */
+    public function getStartTime(): float
+    {
+        if (!$this->isStarted()) {
+            throw new LogicException('Start time is only available after process start.');
+        }
+
+        return $this->starttime;
+    }
+
     /**
      * Returns whether TTY is supported on the current operating system.
      */