patch 9.1.0888: leftcol property not available in getwininfo()

Problem:  leftcol property not available in getwininfo()
Solution: add leftcol property property (glepnir)

closes: #16119

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_bufwintabinfo.vim b/src/testdir/test_bufwintabinfo.vim
index 403b98a..1517a9b 100644
--- a/src/testdir/test_bufwintabinfo.vim
+++ b/src/testdir/test_bufwintabinfo.vim
@@ -115,6 +115,18 @@
   wincmd t | only
 endfunc
 
+function Test_get_wininfo_leftcol()
+  set nowrap
+  set winwidth=10
+  vsp
+  call setline(1, ['abcdefghijklmnopqrstuvwxyz'])
+  norm! 5zl
+  call assert_equal(5, getwininfo()[0].leftcol)
+  bwipe!
+  set wrap&
+  set winwidth&
+endfunc
+
 function Test_get_buf_options()
   let opts = bufnr()->getbufvar('&')
   call assert_equal(v:t_dict, type(opts))