Auto merge of #8768 - vegayours:8616_intermittent_option_unwrap_in_timers, r=jdm

fix intermittent Option::unwrap in timers

fixes intermittent #8616

This intermittent indicates real problem in code.
Lets consider such code:
```javascript
// timer 1
setTimeout(function() {
     //timer 2
     setTimeout(function() {}, 0);
}, 0);
```
When we receive event to fire timer 1 it will be selected and extracted from active timers list in fire_timer function. During timer 1 handler execution we will schedule timer 2 and request timer event for it. But it will be executed during same fire_timer call because of 0 timeout. And as a result we will have empty timers list and expecting event for timer 2 that will crash in assert.

I'm not sure that all I've written is clear, but we have something like this:
```
install timer 1 -> [1] in timers list
push and expect timer event 1 -> expected_event=1
received timer event 1
    fire_timer()
         select timer 1 to execute -> [] in timers list
         execute timer 1 handler
             install timer 2 -> [2] in timers list
             push and expect timer event 2 -> expected_event=2
         select timer 2 to execute (because of 0 timeout) -> [] in tiemrs list
         execute timer 2 handler
expected_event=2 is dangling
received timer event 2
    fire_timer() -> BOOM
```

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tests/wpt/mozilla/meta/MANIFEST.json

@@ -5757,6 +5757,12 @@
             "url": "/_mozilla/mozilla/textcontent.html"
           }
         ],
+        "mozilla/timer_eventInvalidation.html": [
+          {
+            "path": "mozilla/timer_eventInvalidation.html",
+            "url": "/_mozilla/mozilla/timer_eventInvalidation.html"
+          }
+        ],
         "mozilla/title.html": [
           {
             "path": "mozilla/title.html",