The currently active SignatureHelp.
The activeSignatureHelp has its [SignatureHelp.activeSignature] field updated based on
the user arrowing through available signatures.
true if signature help was already showing when it was triggered.
Retriggers occur when the signature help is already active and can be caused by actions such as typing a trigger character, a cursor move, or document content changes.
Character that caused signature help to be triggered.
This is undefined when signature help is not triggered by typing, such as when manually invoking
signature help or when moving the cursor.
Action that caused signature help to be triggered.
Additional information about the context in which a
SignatureHelpProviderwas triggered.