Consider upgrading or deprecating iframe-messenger

[SiAdcock]

We use this in several places (InstagramBlockComponent, UnsafeEmbedBlockComponent, emailEmbed), mainly to allow iframes to ask the parent doc to resize them.

It has not been updated in 10 years, and there are likely to be edge cases we're missing. We could use a well-maintained open source library. See https://github.com/davidjbradshaw/iframe-resizer

[emdash-ie]

Also now used in datawrapper-import (as of https://github.com/guardian/datawrapper-import/pull/4), which will need updating to use any replacement.