Default Admin theme's file_link template does not support empty file_size

Problem/Motivation

Default Admin theme's file-link.html.twig is missing support for cases where the file_size variable is an empty string, due to the with_size variable being FALSE.

Steps to reproduce

If with_size is FALSE, file_size will be empty string, and file-link.html.twig prints empty parentheses as the size. This can be reproduced with the "Table of files" field formatter for a file field.

Proposed resolution

Check that the file_size variable is not empty before printing it.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet