Constrain desktop message height to viewport

[oodarluz]

Hoist React Issue: #3792

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• [ X] Caught up with develop branch as of last change.
• [ X] Added CHANGELOG entry, or determined not required.
• [ X] Reviewed for breaking changes, added breaking-change label + CHANGELOG if so.
• [ X] Updated doc comments / prop-types, or determined not required.
• [ X] Reviewed and tested on Mobile, or determined not required.
• [ X] Created Toolbox branch / PR, or determined not required.

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[amcclain]

Great, thank you for closing this out.