Since vault edit attempts to unlink
edited files before creating a new file
with the same name and writing to it, if
the file was a symlink, the symlink would
be replaced with a regular file.
VaultEditor file ops now check if files
it is changing are symlinks and instead
works directly on the target, so that
os.rename() and shutils do the right thing.
Add unit tests cases for this case and
assorted VaultEditor test cases.
Fixes#20264
6c6b647182