Merge topic 'cmState-policies'

757a1f54 cmState: Move PolicyState from cmMakefile.
52dbe654 cmState: Record the end position of each directory.
65a5e0c6 cmLinkedTree: Add Clear API.
34835433 cmState: Add Type for policy scope.
af0de01c cmState: Remove call stack parent tracking.
6ae8b30b cmMakefile: Move policy barriers inside cmState scopes.
a5fc17b5 cmMakefile: Re-order policy entries and barriers.
0a01e6c6 cmState: Add Snapshot Type accessor.
f0005bb4 Tests: Verify generate-time policy scope behavior.