Implement auto-folding when the user opens a file

[zeroSal]

[outofsync42]

I tried to do this originally, but the file open event triggers every time you switch between tabs for some reason, so it was folding every time you switch tabs. There may be another way or event handler I'm missing. I'll take a look when I get some time and try again.

[outofsync42]

Now I remember what the problem was. I could detect when a file was opened vs tab switched by using first seen but the problem was that if you closed the editor and reopen it, then it triggers again on tabs that were previously open because the variable is reset. I would need to store data in a persistent state relative to the workspace so when its closed and reopened I remember what files were open last time. Again, I'll try and find a work around or a way that is maybe more correct but the API in vscode didn't appear to have a solution at the time I wrote the extension.