Missing selection API

[heruan]

The iron-list element has a selection API that is not accessible from the Flow integration (at least I don't know how). Other than single-item selection, iron-list can also be set to multi-item selection (see iron-list#property-multiSelection).

The Flow IronList component should provide access to these APIs, in the same way as Grid does, e.g. with grid.asMultiSelect().

[web-padawan]

The IronList has been removed in V24. There is a pending PR adding selection API to VirtualList. Closing this as stale.