[web/request] Restore attribute setting for search_state This was dropped in 1f84295bfe95 when `search_state` attribute was turned into a property, but without a setter. So adding a setter here restoring previous behaviour, as some tests and cubes use it. Related to #4875761.

rql('SET X name "BoundaryConstraint" '
    'WHERE X is CWConstraintType, X name "BoundConstraint"')