bug#74914: 30.0.90; Eglot: Incorrect parameter highlighted in signatureHelp

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Felician Nemeth <felician.nemeth@gmail.com>,
>  João Távora <joaotavora@gmail.com>
> From: Troy Brown <brownts@troybrown.dev>
> Date: Mon, 16 Dec 2024 10:19:14 -0500
> 
> I'm working with a language server that provides an `activeParameter`
> field both in SignatureHelp (set to 0) as well as in
> SignatureInformation (set to 1).  Under this condition, for the
> signature output in the echo area, Eglot always displays the first
> parameter (i.e., index 0).  According to the LSP specification, when
> an `activeParameter` field is specified in SignatureInformation "this
> is used in place of `SignatureHelp.activeParameter`".  The following
> is a partial log covering this transaction:
> 
> [jsonrpc] e[09:50:52.423] --> textDocument/signatureHelp[97]
> {"jsonrpc":"2.0","id":97,"method":"textDocument/signatureHelp","params":{"textDocument":{"uri":"file:///home/troy/junk/gtkada_24.0.0_80c56171/src/glib.adb"},"position":{"line":102,"character":38}}}
> [jsonrpc] e[09:50:52.444] <-- textDocument/publishDiagnostics
> {"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"uri":"file:///home/troy/junk/gtkada_24.0.0_80c56171/src/glib.adb","diagnostics":[{"range":{"start":{"line":102,"character":38},"end":{"line":102,"character":39}},"source":"libadalang","message":"Missing
> ';'"},{"range":{"start":{"line":102,"character":38},"end":{"line":102,"character":39}},"source":"libadalang","message":"Skipped
> token )"},{"range":{"start":{"line":0,"character":0},"end":{"line":0,"character":0}},"severity":4,"source":"ada.project","message":""}]}}
> [jsonrpc] e[09:50:52.445] <-- textDocument/hover[95]
> {"jsonrpc":"2.0","id":95,"result":null}
> [jsonrpc] e[09:50:52.454] <-- textDocument/documentHighlight[96]
> {"jsonrpc":"2.0","id":96,"result":null}
> [jsonrpc] e[09:50:52.454] <-- textDocument/signatureHelp[97]
> {"jsonrpc":"2.0","id":97,"result":{"signatures":[{"label":"function
> Internal (Name : String; Thing : String) return
> GType","documentation":"","parameters":[{"label":"Name"},{"label":"Thing"}],"activeParameter":1}],"activeSignature":0,"activeParameter":0}}
> 
> I believe the reason for Eglot's behavior is due to the way
> "active-param" is specified in the cl-loop within `eglot--sig-info`.
> ```text
> with active-param = (or sig-active activeParameter)
> ```
> The value of activeParameter in SignatureInformation (activeParameter)
> should be given higher priority (i.e., listed first) over the
> activeParameter specified in SignatureHelp (sig-active).

João, any comments or suggestions?