Fix missing detection of dead code in expressions

[staabm]

closes phpstan/phpstan#13232
closes phpstan/phpstan#11909

[staabm]

hmm I wonder whether I should add this $isAlwaysTerminating = $isAlwaysTerminating || $result->isAlwaysTerminating(); handling everywhere, where we have

			$hasYield = $hasYield || $result->hasYield();
			$throwPoints = array_merge($throwPoints, $result->getThrowPoints());
			$impurePoints = array_merge($impurePoints, $result->getImpurePoints());

etc...?

edit: I added it in all places where I could think of a example which I was able to test

[staabm]

I think the new behaviour makes sense but the errors are unfortunate

https://github.com/laravel/framework/blob/43993ed92af54aa8620d8e779a7dcd658f44364c/types/Support/Helpers.php#L44-L60

------ ------------------------------------------------------- 
  Line   Support/Helpers.php                                    
 ------ ------------------------------------------------------- 
  47     Unreachable statement - code above always terminates.  
         🪪  deadCode.unreachable                               
  66     Unreachable statement - code above always terminates.  
         🪪  deadCode.unreachable                               
 ------ ------------------------------------------------------- 

[phpstan-bot]

This pull request has been marked as ready for review.