openExternalAsync  
  Opens a link externally using the default application. Depending on the used scheme this can be:
a browser (
http:,https:)a mail client (
mailto:)VSCode itself (
vscode:fromvscode.env.uriScheme)
Note that {@linkcode window.showTextDocument showTextDocument} is the right way to open a text document inside the editor, not this function.
Parameters
target
The uri that should be opened.