Added file URI scheme in Mail helper for resolving absolute paths

What was the issue? 

The issue was when e.g. generating PDF with assets that have file URI schemes, they were replaced by HTTPS/HTTP URI schemes during formatting of asset links.

How did you solve it? 

I’ve solved it by adding an additional condition to skip formatting of file URI scheme leaving it as is because the full path to file will be provided by the developer while adding assets on page with file URI scheme.

Why is this fix important?

It’s important because usage of file URI scheme wasn’t possible before when e.g. rendering PDF from HTML pages. This allows developers more options while planning functionalities similar to the one I described in the issue.

How does it feel to contribute to a platform such as Pimcore? 

It feels good to contribute to Pimcore knowing that your change might help someone and in the end help Pimcore become a better and more reliable platform.

And if you want to check out this pull request, just follow the link!