This change adds logic to push a turnstile event whenever a map view
event is queued. It guards against sending the turnstile event more
than once per session.
Note that `pushTurnstileEvent` is actually a "force push" in that it
flushes the queue and, since it enqueues a turnstile event, the
flush's call to `postEvents` will attempt to send any queued events
even if telemetry is paused. This has the side effect of defeating
the other queue / timing / flush logic in place whenever map load
(and now implicitly turnstile) events are pushed.
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