patch 9.1.1507: symlinks are resolved on :cd commands

Problem:  File paths change from symlink to target path after :cd command
          when editing files through symbolic links
Solution: Add "~" flag to 'cpoptions' to control symlink resolution.
          When not included (default), symlinks are resolved maintaining
          backward compatibility. When included, symlinks are preserved
          providing the improved behavior. (glepnir)

related: neovim/neovim#15695
closes: #17628

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index fcd3b9f..75d1401 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -41643,6 +41643,8 @@
 - 'completeopt' is now a |global-local| option.
 - add 'cpoptions' flag "z" |cpo-z|, to disable some (traditional) vi
   behaviour/inconsistency (see |d-special| and |cw|).
+- add 'cpoptions' flag "~" |cpo-~| to disable resolving symlinks on |:cd|
+  commands
 - new option values for 'fillchars':
 	"trunc"		- configure truncation indicator, 'pummaxwidth'
 	"truncrl"	- like "trunc" but in 'rl' mode, 'pummaxwidth'