Add an EditorInfo field to $psEditor

[rjmholt]

We should add a simple info object to $psEditor so information like editor name and version can be queried from $psEditor. Since we should theoretically support many editors, we could require a few standard fields or we could just make it an object and let editors decide what information they provide.

I'm not saying we should try to implement ISEOptions here as that would be a lot more work. Just an information field along the lines of $PSVersionTable.

[rjmholt]

For reference: PowerShell/vscode-powershell#773