CVSS 4.0 calculator on advisory improvement screen does not support non-base metrics

[mhassan1]

The CVSS 4.0 calculator on the advisory improvement screen does not support non-base (i.e. threat, environmental, and supplemental) metrics, as defined in the spec. There are a couple problems with this:

1. The calculator does not consider them in its calculation of severity (I'm not sure how big of a problem this is)
2. It's not possible to submit the advisory improvement request if any of those metrics is present (even if it is already present)

Here's an example of a PR where I was required to remove the E threat metric, even though that wasn't something that I wanted to do, in order to submit the page. With the E metric there, I see an error (The entered vector string contains an error and cannot populate a score.).