Embedded Custom Viz does not receive options from embed JS update events

[colin-roy-ehri]

When embedding a Dashboard with a custom visualization, the JS dashboard:options:set event does not update the visualization options.
I've tried this with the embed SDK, simple JS events, and the dynamic dashboard tester. @bryan-at-looker helped me confirm the issue.

Effect:
This issue prevents dynamically updating embedded custom visualizations.

To reproduce:

1. Create any custom visualization with a new option and console.log(options) inside the updateAsync function.
2. Create a dashboard using that custom visualization.
3. Add the viz to a looker instance and run the application dynamic dashboard tester.
4. Inside the dynamic dashboard tester, locate your new dashboard from step 2 and change the custom option from step 1.
5. Notice that the logged options in the console do not change.