OptionalinitialPosition: { pos: Point; prefix: string }Optionaloptions: CompletionProviderOptionsOptionaloptions: CompletionProviderOptionsThis is the entry point to the class, it gathers, then provides the completions asynchronously via callback.
The callback function may be called multiple times, the last invokation is marked with a finished flag
This class is responsible for providing completions and inserting them to the editor