feat(api): more fields in nvim_list_uis

Problem:
nvim_list_uis does not report all ":help ui-option" fields.

Solution:
Store ":help ui-option" fields on the `UI` object and update ui_array.

src/nvim/ui_client.c

@@ -1,6 +1,8 @@
 // This is an open source non-commercial project. Dear PVS-Studio, please check
 // it. PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
 
+/// Nvim's own UI client, which attaches to a child or remote Nvim server.
+
 #include <stdbool.h>
 #include <stdint.h>
 #include <stdlib.h>