add numeric icon feature

[dkuntze]

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This PR expands the ability to have numbers in icon names while keeping existing functionality. It does fail the regex vulnerability check at https://devina.io/redos-checker (but so does the existing). Will look at seeing if its possible to refactor to make it free of vulnerabilities by making this a tokenizer statemachine.

Related Issues

Thanks for contributing!

[tripodsan]

sorry, but we need to do a full scan of all content of all customers in order to judge the scope of this change. the last time, we created a CSO with exactly this kind of fix.

[alexcarol]

This will also be useful for the ESRI project, thanks @dkuntze!