Run qa:selectors-as-if-foss in frontend/QA MRs

What does this MR do and why?

Runs the qa:selectors-as-if-foss job in all MRs that change page objects or the frontend views they represent.

• Renames .qa:rules:as-if-foss to .qa:rules:selectors-as-if-foss because qa:selectors-as-if-foss is the only job it's used in.

Closes #432509 (closed)

Test pipelines

In an MR with a:

• FE change (qa:selectors-as-if-foss included - fail expected): https://gitlab.com/gitlab-org/gitlab/-/pipelines/1079507110
• BE change (qa:selectors-as-if-foss not included): https://gitlab.com/gitlab-org/gitlab/-/pipelines/1079562611
• QA change (qa:selectors-as-if-foss included - fail expected): https://gitlab.com/gitlab-org/gitlab/-/pipelines/1079521933
• Docs change (qa:selectors-as-if-foss not included): https://gitlab.com/gitlab-org/gitlab/-/pipelines/1079536389

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.