Add display handling of files added by git add -N

[ChristianAlexander]

Relates to #42665

Adds support for displaying files which were added by git add -N.

According to man git-add:

-N, --intent-to-add
           Record only the fact that the path will be added later. An entry for the path is placed in the
           index with no content. This is useful for, among other things, showing the unstaged content of
           such files with git diff and committing them with git commit -a.

As files in this state are only present in the working tree (and not the index or a part of any merge behavior), this change adds them to the workingTree section of the git UI (usually localized as "Changes").

Because there is no previous version of the file available, only a right entry in the editor is created when opened, just like files which have a status of UNTRACKED.

Before:

After:

[joaomoreno]

Thanks! 🍻