feat(api): set nvim_echo() kind for ext_messages (#33998)

Problem:  Unable to emit a message with arbitrary kind.
Solution: Add a "kind" opts field to nvim_echo().
          Use it to set the "list_cmd" kind for vim.show_pos().

runtime/lua/vim/_meta/api.lua

@@ -1101,6 +1101,7 @@ function vim.api.nvim_del_var(name) end
 --- @param history boolean if true, add to `message-history`.
 --- @param opts vim.api.keyset.echo_opts Optional parameters.
 --- - err: Treat the message like `:echoerr`. Sets `hl_group` to `hl-ErrorMsg` by default.
+--- - kind: Set the `ui-messages` kind with which this message will be emitted.
 --- - verbose: Message is controlled by the 'verbose' option. Nvim invoked with `-V3log`
 ---   will write the message to the "log" file instead of standard output.
 function vim.api.nvim_echo(chunks, history, opts) end