Consider relying upon $TERM_PROGRAM=vscode

[Tyriar]

Testing #226

I see this was added to my pwsh profile:

#region vscode python
if ($null -ne $env:VSCODE_PWSH_ACTIVATE) {
    Invoke-Expression $env:VSCODE_PWSH_ACTIVATE
}
#endregion vscode python

I think you should also block this by TERM_PROGRAM to make sure this only ever runs inside VS Code. You can see examples of this in the shell integration manual install docs: https://code.visualstudio.com/docs/terminal/shell-integration#_manual-installation

[karthiknadig]

Fixed via #196