How a {@linkcode SignatureHelpProvider} was triggered.
Variables
read onlyContentChange:SignatureHelpTriggerKind
Signature help was triggered by the cursor moving or by the document content changing.
read onlyInvoke:SignatureHelpTriggerKind
Signature help was invoked manually by the user or by a command.
read onlyTriggerCharacter:SignatureHelpTriggerKind
Signature help was triggered by a trigger character.