Fix flaky quick_action_suggestions frame-guard spec

What does this MR do and why?

Backport the spec fix from !242910 (merged). This fixes a flaky test in spec/frontend/editor/quick_action_suggestions_spec.js where the test attempted to mock global.performance to verify that a deduplication guard works correctly. However, in jsdom the performance property is read-only, so the mock assignment had no effect and the code continued reading from the real advancing clock. When consecutive calls crossed a 16 millisecond frame boundary, the guard intermittently failed. The fix spies on performance.now instead, pinning the frame boundary and making the guard deterministic. This is a test-only change with no impact to product code.

The fix is already present in master and 19-2-stable-ee. It is missing from 19-1-stable-ee (this MR) and 19-0-stable-ee (backported separately in !249374 (merged)).

MR acceptance checklist

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
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• Ensure the e2e:test-on-omnibus-ee job has succeeded, or if it has failed, investigate the failures. If you determine the failures are unrelated, you may proceed. If you need assistance investigating, request help in the #s_developer_experience Slack channel to confirm the failures are unrelated to the merge request.

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