Represents the signature of something callable. A signature can have a label, like a function-name, a doc-comment, and a set of parameters.
The index of the active parameter.
If provided, this is used in place of SignatureHelp.activeParameter.
The human-readable doc-comment of this signature. Will be shown in the UI but can be omitted.
The label of this signature. Will be shown in the UI.
The parameters of this signature.