Also use signature label offsets for parameter info
According to the LSP specification, a parameter of a callable-signature
has a label and a optional doc-commet. The label of a parameter
information is either a string or an inclusive start and exclusive end
offsets within its containing signature label.
Previously, this was only taken in account for highlighting the
parameter in the definition signature.
* eglot.el (eglot--sig-info): Handle signature label offsets
when printing the signature parameter information.