vim-patch:9.1.0785: cannot preserve error position when setting quickfix list (#30820)

Problem:  cannot preserve error position when setting quickfix lists
Solution: Add the 'u' action for setqflist()/setloclist() and try
          to keep the closes target position (Jeremy Fleischman)

fixes: vim/vim#15839
closes: vim/vim#15841

27fbf6e5e8

Co-authored-by: Jeremy Fleischman <jeremyfleischman@gmail.com>

runtime/lua/vim/_meta/vimfn.lua

@@ -8229,6 +8229,8 @@ function vim.fn.setpos(expr, list) end
 ---   clear the list: >vim
 ---     call setqflist([], 'r')
 --- <
+--- 'u'  Like 'r', but tries to preserve the current selection
+---   in the quickfix list.
 --- 'f'  All the quickfix lists in the quickfix stack are
 ---   freed.
 ---