ASP-based solver: account for deprecated versions (#23491)

fixes #22351

The ASP-based solver now accounts for the presence
in the DAG of deprecated versions and tries to minimize
their number at highest priority.

var/spack/repos/builtin.mock/packages/deprecated-versions/package.py

@@ -0,0 +1,12 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+class DeprecatedVersions(Package):
+    """Package with the most recent version deprecated"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/c-1.0.tar.gz"
+
+    version('1.1.0', '0123456789abcdef0123456789abcdef', deprecated=True)
+    version('1.0.0', '0123456789abcdef0123456789abcdef')