feat(ui): vim.ui.img api #37914

Problem:
No builtin api to load and display images.

Solution:
Introduce vim.ui.img. Only supports kitty graphics protocol, currently.

runtime/lua/vim/ui.lua

@@ -1,4 +1,6 @@
-local M = {}
+local M = vim._defer_require('vim.ui', {
+  img = ..., --- @module 'vim.ui.img'
+})
 
 ---@class vim.ui.select.Opts
 ---@inlinedoc