vim-patch:9.1.1477: no easy way to deduplicate text

Problem:  no easy way to deduplicate text
Solution: add the :uniq ex command
          (Hirohito Higashi)

closes: vim/vim#17538

74f0a77bb9

Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>

runtime/lua/vim/_meta/vimfn.lua

@@ -10612,6 +10612,7 @@ function vim.fn.undotree(buf) end
 ---   let newlist = uniq(copy(mylist))
 --- <The default compare function uses the string representation of
 --- each item.  For the use of {func} and {dict} see |sort()|.
+--- For deduplicating text in the current buffer see |:uniq|.
 ---
 --- Returns zero if {list} is not a |List|.
 ---