Test: Provide command to open most recently closed file/editor

[Tyriar]

Test plan for #3989

• Test Linux @isidorn
• Test Windows @bpasero
• Test OS X @kieferrm

This feature is supposed to reopen working files that are removed from the working files list. It does not work for preview files that are not yet in the working files list. This feature contributes a command (ctrl+shift+t) and a menu item in File > Open Recent.

Basic test

1. Open 2 working files, A then B
2. Remove A then B from working files
3. ctrl+shift+t should restore B
4. ctrl+shift+t should restore A

Basic test (close all files)

1. Open multiple working files, note the currently active file in the editor
2. Run command workbench.files.action.closeAllFiles (default: ctrl+k ctrl+w
3. ctrl+shift+t should restore the previously active file
4. ctrl+shift+t should restore the rest of the files (in no particular order)

Interesting cases

I tried to cover a range of cases, here are some of the interesting ones:

• Split editors
• Removing a working file, reopening it and then attempting to restore (it should be skipped and the previously closed working file should be restored)
• Deleting files before they are scheduled to be reopened