Add fuzzy file finder to the Web IDE

In large projects it is much more practical to open files using a fuzzy finder. For this reason nearly all modern editors off fuzzy file finding out of the box. GitLab even has one in the repo view: https://docs.gitlab.com/ee/workflow/file_finder.html

We should add support for fuzzy file finding to the multi-file editor.

Design

We can use a similar UI as to the file finder in the merge request diff tab:

• When first opening the file finder, let's provision it with 2-4 recently closed files if possible
• Let's get the icons and file path in there as well similar to atom

This will get us to:

Let's get the same hotkey functional if possible: t (if editor is not selected)