Windows permissions: uninstalling and cleaning stages (#29714)

When running on Windows, Spack may generate files in the stage/install
prefixes that do not have write permissions, which prevents the
removal of those directories (e.g. when cleaning stages or uninstalling).
There should be a refactoring to avoid this in the first place, but that
is assumed to be longer term, so the temporary fix is to make such files
writable if they are not. This PR:

* Automatically handles these permissions errors when uninstalling
  packages from the Spack root (makes then writable)
* Updates similar already-existing logic when removing Spack-managed
  stage directories (the error-handling was assuming all errors were
  permissions errors and was therefore handling other errors
  inappropriately)

Note: these permissions issues only appear on Windows so this logic is
only applied there (permissions are not modified for this purpose on
Linux etc.).

This also adds special handling for a case where calling `isdir`
on an `os.DirEntry` object would fail for improperly-created symlinks
(e.g. on Windows, using `os.symlink` without `target_is_directory=True`).
Note this specific issue only came up when enabling link_tree tests
(specifically `source_merge_visitor_cant_be_cyclical`).

0 files changed, 0 insertions, 0 deletions