onDidOpenTextDocument
An event that is emitted when a text document is opened or when the language id of a text document languages.setTextDocumentLanguage.
To add an event listener when a visible text document is opened, use the TextEditor events in the window namespace. Note that:
The event is emitted before the document is updated in the active text editor
When a text document} is already open (e.g.: open in another {@link window.visibleTextEditors visible text editor) this event is not emitted