Leaking events when element containing a "BaseExperienceFrame" gets destroyed

[kfrancois]

Steps to reproduce

1. Clone and set up https://github.com/kfrancois/repro-amazon-quicksight-embedding-sdk

git clone https://github.com/kfrancois/repro-amazon-quicksight-embedding-sdk.git
npm i
npm start

2. Plug in your own QSearchBar url here
3. Wait for the app to load
4. Click on the "Hide container"-button

Result

Every page click will throw a CLOSE_Q_SEARCH timed out-error.
This is because BaseExperienceFrame adds a mutation observer on the body element, but this mutation observer only checks for node === this.iframe || node === this.container.
Because of this, if the parent element of the container element (or any of its parents) get removed from the DOM, no cleanUpCallbacks actually execute.

This feels like unexpected behaviour as there are leaky object references & event listeners that stay active even after the embedded Quicksight element is destroyed.

[kfrancois]

Potentially, we could use document.body.contains(node) instead of checking for equality on a removed node, but I'm not sure about possible performance implications here (since we're traversing the DOM on every mutation).