Set environment variable `WT_FOLDER_PATH` to the folder path that contains `WindowsTerminal.exe`

[daxgames]

Description of the new feature/enhancement

Set an environment variable WT_FOLDER_PATH to the folder path that contains WindowsTerminal.exe. This variable should be set when Windows Terminal launches before the profile is launched.

This would be useful for users that run Windows Terminal in portable mode so Windows terminal profiles can be configured with paths relative to the folder wher WIndows Terminal is installed as shown below:

The normal user profile is configured as shown below and works perfectly because the %CMDER_ROOT% env variable was set dynamically before launching Windows Terminal.

The above configuration does not work when launching as Administrator because the %CMDER_ROOT% env variable is not set globally on the system nor in the Administator's personal environment variables. it produces the error below:

For completeness sake the icon config being complained about in the error above is below:

Proposed technical implementation details (optional)

[zadjii-msft]

This really falls under the same problem space as #13006 et al. We could add that, sure,

Wait, no it doesn't. This is actually so simple. Set that variable for terminal itself. So that we can resolve things relative to ourself. brilliant.

I think we were already tracking this in #15379 but I'll motion to use this as the tracking thread instead, since this has a real good idea. Thanks!