Helper module to handle PHP in translations

In #357529: Implement translation of customized 'translatable' views properties we came across an issue to do with PHP in translations.

Some strings that need to be translated have a filter format, which can include the PHP filter.

Passing these to translation can both (a) expose sensitive data and (b) enable users without PHP access (translators) to alter or inject new PHP.

What to do? The attached draft module uses the following approach:

(a) replace PHP with placeholders before sending for translation,

(b) fetch translated versions and strip out PHP,

(c) substitute back in the original PHP for the placeholders.

This might be a good addition to i18n because we could use it in other places, e.g., in custom blocks that are being translated with tt() and might contain PHP.

From the code documentation:

This module implements two hooks. As with hook_nodeapi(), implementations of these hooks need to both pass by reference and return values. For this reason they can't be invoked with module_invoke_all(). Instead, module authors wanting to use these hooks should include a method like the following in their modules:

function example_invoke_translation_process(&$value, $arg, $op) {
   $return = array();
   $hook = 'translation_' . $op . '_process';
   foreach (module_implements($hook) as $module) {
     $function = $module . '_' . $hook;
     $result = $function($value, $arg);
     if (isset($result)) {
       $return[$module] = $result;
     }
   }
   return $return;
}

Then, to ensure that any strings with associated filters are safely handled, follow these two steps:

1. Call 'pre' processing before sending for translation.

$translation_data = example_invoke_translation_process($string, $format, 'pre');

In this call, $string is the string to be translated and $format is the ID of the filter format to be applied.

2. Call 'post' processing after sending for translation.

example_invoke_translation_process($string, $translation_data, 'post');

In this call, $string is the string to be translated and $translation_data is the data returned from the previous call.