Problem: setting `loclist = true` makes `on_list` being ignored. This
was not a problem before, but with `vim.lsp.buf.document_symbol` using
`loclist = true` as default it is needed to explicitly pass `loclist =
false` in order to use custom `on_list`.
Solution: prefer `on_list` over `loclist` and document the latter as
taking effect only in the default handler.