Fix(web-react): Warn when icon asset is missing from the map

[literat]

Description

Raise a warning when there is no icon content to be provided. Also, check more strictly the fallback icon and return only when the fallback is matched. Otherwise, raise a warning and return an empty string.

Additional context

• https://almamedia.slack.com/archives/C068XPSDWQN/p1715860777231279

Issue reference

[netlify]

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[literat]

• Add test for this.

[literat]

@pavelklibani @curdaj @crishpeen This will conflict with the release branch because I think the same problem is similar there. So after the merge, I will do a rebase and fix the future conflict.

[coveralls]

coverage: 79.544% (+0.1%) from 79.429%
when pulling 031c64a on fix/warn-from-icon-bad-mapgco
into c9797b5 on main.