Save mirador instances in the DOM

[joecorall]

What does this Pull Request do?

Save mirador instance in drupalSettings so other modules can use mirador's store/dispatch.

• Related GitHub Issue: (link)

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  Release pull requests, etc.)

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[alxp]

What am I missing here?

Not seeing the instances. (I'm not logged in if that makes a difference.)

[adam-vessey]

Just grabbed it locally here, applied patch-wise, cleared cache, and it seems to be there?: