feat: Add callback parameter to LspRequestCustom

This change allows to provide callback function to custom requests.

Author: blami

autoload/lsp/lspserver.vim

@@ -1041,13 +1041,14 @@ enddef
 # Name: name of the server
 # Request: any
 # Params: any
-def g:LspRequestCustom(name: string, msg: string, params: any): string
+# Cbfunc: callback function
+def g:LspRequestCustom(name: string, msg: string, params: any, Cbfunc: func): string
   var lspserver: dict<any> = buf.CurbufGetServerByName(name)
   if lspserver->empty()
     return ''
   endif
 
-  lspserver.rpc_a(msg, params, WorkspaceExecuteReply)
+  lspserver.rpc_a(msg, params, Cbfunc)
   return ''
 enddef