GenEx: Evaluate LINK_LIBRARIES target properties transitively

The `LINK_LIBRARIES` and `INTERFACE_LINK_LIBRARIES` target properties
establish the graph of link dependencies used to propagate usage
requirements transitively.  Therefore the `$<TARGET_PROPERTY:...>`
generator expression should evaluate them transitively as it does for
other transitive properties.  Add policy CMP0189 for compatibility.

Fixes: #26709
Issue: #12435