So far, the scripting API was using events to communicate between WA and the iFrame.
But often, the scripting API might actually want to "ask" WA a question and wait for an answer.
We dealt with this by using 2 unrelated events (in a mostly painful way).
This commit adds a "queryWorkadventure" utility function in the iFrame API that allows us
to send a query, and to wait for an answer. The query and answer events have a unique ID to be
sure the answer matches the correct query.
On the WA side, a new `IframeListener.registerAnswerer` method can be used to register a possible answer.
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