minor #14937 Standardize the name of the exception variables (javiereguiluz)

This PR was squashed before being merged into the 2.3 branch (closes #14937).

Discussion
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Standardize the name of the exception variables

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

See symfony/symfony-docs#4491 for the context of this change.

In Symfony source code there are 410 `try ... catch` blocks. More than 95% of them use `$e` as the name of the exception variable. After applying these changes, 407 out of 410 variables are named `$e`.

These are the three cases where I didn't change the name of the `$e` variable:

  * Nested exception in https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/Routing/Matcher/RedirectableUrlMatcher.php#L40. It uses `$e2` as the name of the nested variable.
  * Nested exception in https://github.com/symfony/symfony/blob/2.3/src/Symfony/Bundle/TwigBundle/TwigEngine.php#L82. I changed the name of the `$ex` variable to `$e2` to match the previous syntax.
  * https://github.com/symfony/symfony/blob/2.3/src/Symfony/Component/Console/Helper/DialogHelper.php#L463. I don't know if it's safe to change the name of the `$error` exception variable.

Commits
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e8b924c Standardize the name of the exception variables

Author: fabpot

Compiler/ResolveInvalidReferencesPass.php

@@ -47,7 +47,7 @@ public function process(ContainerBuilder $container)
             foreach ($definition->getMethodCalls() as $call) {
                 try {
                     $calls[] = array($call[0], $this->processArguments($call[1], true));
-                } catch (RuntimeException $ignore) {
+                } catch (RuntimeException $e) {
                     // this call is simply removed
                 }
             }
@@ -58,7 +58,7 @@ public function process(ContainerBuilder $container)
                 try {
                     $value = $this->processArguments(array($value), true);
                     $properties[$name] = reset($value);
-                } catch (RuntimeException $ignore) {
+                } catch (RuntimeException $e) {
                     // ignore property
                 }
             }