minor #30296 [VarDumper] link paths in stack traces to IDE (nicolas-grekas)

This PR was merged into the 4.3-dev branch.

Discussion
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[VarDumper] link paths in stack traces to IDE

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | not really
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

`./test.php:8` and `./test.php:11` can now be clicked:

![image](https://user-images.githubusercontent.com/243674/52971041-466b1c80-33b6-11e9-9bc1-0e55dc115f63.png)

Commits
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6672ac3f43 [VarDumper] link paths in stack traces to IDE

src/Symfony/Component/VarDumper/Caster/ExceptionCaster.php

@@ -236,7 +236,7 @@ class ExceptionCaster
                             $ellipsis += 1 + \strlen($f['line']);
                         }
                     }
-                    $srcAttr .= '&separator= ';
+                    $srcAttr .= sprintf('&separator= &file=%s&line=%d', rawurlencode($f['file']), $f['line']);
                 } else {
                     $srcAttr .= '&separator=:';
                 }