Improve detection of droppers, stealers & obfuscated scripts

[tstromberg]

This PR is focused on improving our results for recent threat research:

• https://blog.xlab.qianxin.com/uncovering_darkcracks_payload_delivery_framework_cn/
• https://blog.phylum.io/north-korea-still-attacking-developers-via-npm/

Related samples PR: https://github.com/chainguard-dev/bincapz-samples/pulls/4