Handle errors when PHP code executes

@thanks for contributing! This could be an useful feature. A quick review:

1. +++ b/src/Form/ExecutePHP.php
   @@ -4,6 +4,8 @@ namespace Drupal\devel\Form;
   +use ParseError;
   +use Error;
   

   I think that the coding standard for using this class is use FQNS (\ParseError, \Error - without using the use statement)

2. +++ b/src/Form/ExecutePHP.php
   @@ -45,11 +47,20 @@ class ExecutePHP extends FormBase {
   +    catch (ParseError $error) {}
   +    catch (Error $error) {}
   +
   +    if (isset($error)) {
   +      drupal_set_message($error->getMessage(), 'error');
   +    }
   

   there is a reason for catching the two error separately? looking at the Error hierarchy ParseError extends Error.. so probably we can simply write the code like :

   } 
   catch (\Error $error) {
     drupal_set_message($error->getMessage(), 'error');
   }

   I'm missing something?

and probably we need to write a little test for this :)

[#3005475: Remove Execute PHP feature]

Code moved due to #3005475-15: Remove Execute PHP feature.

Committed and pushed to 8.x-1.x
Thank you!