[Utils] Separate update-verify-tests script from core

The script no longer attempts to be RUN line aware. Feeding raw llvm-lit
output into it _may_ still work, but given a large enough number of
test cases to update, the risk that some test case uses unsupported
features grows pretty large. This will instead be handled by adding a
lit integration to automatically invoke the core for each failing test
output. The lit integration will be landed as a separate change.

Author: hnrklssn