Send {expr} over {handle}. The {expr} is encoded according to the type of channel. The function cannot be used with a raw channel. See |channel-use|. {handle} can be a Channel or a Job that has a Channel. When using the "lsp" channel mode, {expr} must be a |Dict|. If the channel mode is "lsp", then returns a Dict. Otherwise returns an empty String. If the "callback" item is present in {options}, then the returned Dict contains the ID of the request message. The ID can be used to send a cancellation request to the LSP server (if needed). Returns an empty Dict on error. If a response message is not expected for {expr}, then don't specify the "callback" item in {options}. Can also be used as a |method|: GetChannel()->ch_sendexpr(expr)