vim-patch:7.4.1557 (#5117)

Problem:    Windows cannot be identified.
Solution:   Add a unique window number to each window and functions to use it.

86edef664e

src/nvim/version.c

@@ -720,7 +720,7 @@ static int included_patches[] = {
   // 1560 NA
   // 1559,
   // 1558,
-  // 1557,
+  1557,
   // 1556 NA
   // 1555 NA
   1554,