CursorHold continuously fails if LSP does not support textDocument/documentSymbol

[WhyNotHugo]

Error detected while processing CursorHold Autocommands for "<buffer=1>":                                                                      
method textDocument/documentSymbol is not supported by any of the servers registered for the current buffer

I think the right to do here is to check that the server has this capability before sending the request (perhaps this can be done just once per buffer?).