Enable `assumeImmutableResults` for the MR Popover

What does this MR do and why?

For #338435 (closed)

Enables the Apollo assumeImmutableResults construction option for the mr_popover utility/component.

Screenshots or screen recordings

Nothing has changed in the UI and everything is fine there's nothing to see here.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

But not required, am I right?

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.