Update status and policy drawer tab titles

What does this MR do and why?

This MR is a follow-up of !119738 (comment 1382584674).

It updates wording for vulnerability states and a policy drawer tab.

Screenshots or screen recordings

Needs triage:

YAML tab:

How to set up and validate locally

1. Ensure the GitLab Ultimate license is enabled
2. Navigate to a project/group => Security & Compliance => Policies => New policy => Scan result policy
3. Statuses for both New and Previously existing should state Needs triage instead of Needs Triage
4. Create a new policy
5. Click on the new policy in the policies list
6. The tab title should read YAML

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

/cc @rdickenson

Related to #396985 (closed)