Provide help for the signature at the given position and document.
The document in which the command was invoked.
The position at which the command was invoked.
A cancellation token.
Information about how signature help was triggered.
Signature help or a thenable that resolves to such. The lack of a result can be
signaled by returning undefined
or null
.
The signature help provider interface defines the contract between extensions and the parameter hints-feature.