Function GetEffectiveAlternateBaseViewName

Returns the effective semantic AlternateBaseView name for a RunViewParams object:

• An explicit non-empty params.AlternateBaseView takes precedence over a saved User View's pinned DisplayState.alternateBaseView on params.ViewEntity.
• An explicit empty params.AlternateBaseView: "" overrides a saved User View's pin back to BaseView (returns undefined without falling back to params.ViewEntity).
• When params.AlternateBaseView is undefined, falls back to params.ViewEntity's pinned DisplayState.alternateBaseView.